Online Etymology Dictionary

expiate (v.): c. 1600 (OED 2nd ed. print entry has a typographical error in the earliest date), from Latin expiatus, past participle of expiare "to make amends, atone for" (see expiation). Related: Expiable (1560s); expiated; expiating.
expiation (n.): early 15c., via Middle French expiation or directly from Latin expiationem (nominative expiatio) "satisfaction, atonement," noun of action from past participle stem of expiare "make amends for, atone for; purge by sacrifice, make good," from ex- "completely" (see ex-) + piare "propitiate, appease," from pius "faithful, loyal, devout" (see pious).
The sacrifice of expiation is that which tendeth to appease the wrath of God. [Thomas Norton, translation of Calvin's "Institutes of Christian Religion," 1561]
expiatory (adj.): 1540s, from Late Latin expiatorius, from expiat-, past participle stem of Latin expiare "make amends" (see expiation).
expiration (n.): early 15c., "vapor, breath," from Middle French expiration, from Latin expirationem/exspirationem (nominative expiratio/exspiratio) "a breathing out, exhalation," noun of action from past participle stem of expirare/exspirare "breathe out; breathe one's last" (see expire). Meaning "termination, end, close" is from 1560s.
expire (v.): c. 1400, "to die," from Old French expirer "expire, elapse" (12c.), from Latin expirare/exspirare "breathe out, blow out, exhale; breathe one's last, die," hence, figuratively, "expire, come to an end, cease," from ex- "out" (see ex-) + spirare "to breathe" (see spirit (n.)). "Die" is the older sense in English; that of "breathe out" is first attested 1580s. Of laws, patents, treaties, etc., mid-15c. In 17c. also transitive. Related: Expired; expiring.
expiry (n.): "close, termination," 1752, from expire + -y (4). Meaning "dying, death" is from 1790.
explain (v.): early 15c., from Latin explanare "to explain, make clear, make plain" (see explanation). Originally explane, spelling altered by influence of plain. Also see plane (v.2). In 17c., occasionally used more literally, of the unfolding of material things: Evelyn has buds that "explain into leaves" ["Sylva, or, A discourse of forest-trees, and the propagation of timber in His Majesties dominions," 1664]. Related: Explained; explaining; explains. To explain (something) away is from 1709.
explainable (adj.): c. 1600, from explain + -able.
explanation (n.): late 14c., from Latin explanationem (nominative explanatio) "an explanation, interpretation," noun of action from past participle stem of explanare "to make plain or clear, explain," literally "make level, flatten," from ex- "out" (see ex-) + planus "flat" (see plane (n.1)).
explanatory (adj.): 1610s, from or modeled on Late Latin explanatorius "having to do with an explanation," from Latin explanat-, past participle stem of explanare "make plain or clear" (see explanation).
expletive (n.): 1610s, "a word or phrase serving to fill out a sentence or metrical line," from Middle French explétif (15c.) and directly from Late Latin expletivus "serving to fill out," from explet-, past participle stem of Latin explere "fill out, fill up, glut," from ex- "out" (see ex-) + plere "to fill" (see pleio-).

Sense of "an exclamation," especially "a curse word, an oath," first recorded 1815 in Sir Walter Scott, popularized by edited transcripts of Watergate tapes (mid-1970s), in which expletive deleted replaced President Nixon's salty expressions. As an adjective, from 1660s.
expletive (adj.): mid-15c., in grammar, "correlative," from Latin expletivus "serving to fill out" (see expletive (n.)).
explicable (adj.): 1550s, from or modeled on Latin explicabilis "capable of being unraveled, that may be explained," from explicare "unfold; explain" (see explicit). Middle English had a verb expliken "explain, interpret" (mid-15c.).
explicate (v.): "give a detailed account of," 1530s, from Latin explicatus, past participle of explicare "unfold, unravel, explain" (see explicit). Related: Explicated; explicating.
explication (n.): 1520s, from Middle French explication, from Latin explicationem (nominative explicatio), noun of action from past participle stem of explicare "unfold; explain" (see explicit).
explicative (adj.): 1640s, "having the function of explaining," from Latin explicativus, from explicat-, past participle stem of explicare "unfold; explain" (see explicit). As a noun, from 1775.
explicit (adj.): 1610s, "open to the understanding, not obscure or ambiguous," from French explicite, from Latin explicitus "unobstructed," variant past participle of explicare "unfold, unravel, explain," from ex- "out" (see ex-) + plicare "to fold" (see ply (v.1)). As a euphemism for "pornographic" it dates from 1971. Related: Explicitness. "Explicitus" was written at the end of medieval books, originally short for explicitus est liber "the book is unrolled."
explicitly (adv.): 1630s, from explicit + -ly (2). Opposed to implicitly.
explode (v.): 1530s (transitive), "to reject with scorn," from Latin explodere "drive out or off by clapping, hiss off, hoot off," originally theatrical, "to drive an actor off the stage by making noise," hence "drive out, reject, destroy the repute of" (a sense surviving in an exploded theory), from ex- "out" (see ex-) + plaudere "to clap the hands, applaud," which is of uncertain origin. Athenian audiences were highly demonstrative. clapping and shouting approval, stamping, hissing, and hooting for disapproval. The Romans seem to have done likewise.
At the close of the performance of a comedy in the Roman theatre one of the actors dismissed the audience, with a request for their approbation, the expression being usually plaudite, vos plaudite, or vos valete et plaudite. [William Smith, "A First Latin Reading Book," 1890]
English used it to mean "drive out with violence and sudden noise" (1650s), later "cause to burst suddenly and noisily" (1794). Intransitive sense of "go off with a loud noise" is from 1790, American English; figurative sense of "to burst with destructive force" is by 1882; that of "burst into sudden activity" is from 1817; of population by 1959. Related: Exploded; exploding.
exploit (n.): late 14c., "outcome of an action," from Old French esploit "a carrying out; achievement, result; gain, advantage" (12c., Modern French exploit), a very common word, used in senses of "action, deed, profit, achievement," from Latin explicitum "a thing settled, ended, or displayed," noun use of neuter of explicitus, past participle of explicare "unfold, unroll, disentangle" (see explicit).

Meaning "feat, achievement" is c. 1400. Sense evolution is from "unfolding" to "bringing out" to "having advantage" to "achievement." Related: Exploits.
exploit (v.): c. 1400, espleiten, esploiten "to accomplish, achieve, fulfill," from Old French esploitier, espleiter "carry out, perform, accomplish," from esploit (see exploit (n.)). The sense of "use selfishly" first recorded 1838, from a sense development in French perhaps from use of the word with reference to mines, etc. (compare exploitation). Related: Exploited; exploiting.
exploitation (n.): 1803, "productive working" of something, a positive word among those who used it first, though regarded as a Gallicism, from French exploitation, noun of action from exploiter (see exploit (v.)). Bad sense developed 1830s-50s, in part from influence of French socialist writings (especially Saint Simon), also perhaps influenced by use of the word in U.S. anti-slavery writing; and exploitation was hurled in insult at activities it once had crowned as praise.
It follows from this science [conceived by Saint Simon] that the tendency of the human race is from a state of antagonism to that of an universal peaceful association -- from the dominating influence of the military spirit to that of the industriel one; from what they call l'exploitation de l'homme par l'homme to the exploitation of the globe by industry. ["Quarterly Review," April & July 1831]
exploitative (adj.): 1882, from French exploitatif, from exploit (see exploit (n.)). Alternative exploitive (by 1859) appears to be a native formation from exploit + -ive.
exploration (n.): 1540s, from Middle French exploration and directly from Latin explorationem (nominative exploratio) "an examination," noun of action from past participle stem of explorare "investigate, examine" (see explore). Alternative explorement is from 1640s.
exploratory (adj.): mid-15c., from Latin exploratorius "belonging to scouts," from explorator "scout," from explorare "investigate, examine" (see explore). Alternative explorative is from 1738; explorational is from 1889.
explore (v.): 1580s, "to investigate, examine," a back-formation from exploration, or else from Middle French explorer (16c.), from Latin explorare "investigate, search out, examine, explore," said to be originally a hunters' term meaning "set up a loud cry," from ex- "out" (see ex-) + plorare "to weep, cry." Compare deplore. However, de Vaan notes that "the ancient explanation, ... that the verb explorare originally meant 'to scout the hunting area for game by means of shouting'" is now considered "unlikely." Second element also is explained as "to make to flow," from pluere "to flow." Meaning "to go to a country or place in quest of discoveries" is first attested 1610s. Related: Explored; exploring.
explorer (n.): 1680s, agent noun from explore. Replaced earlier exploratour (mid-15c.).
explosion (n.): 1620s, "action of driving out with violence and noise," from French explosion, from Latin explosionem (nominative explosio) "a driving off by clapping," noun of action from past participle stem of explodere "drive out by clapping" (see explode for origin and sense evolution). Meaning "a going off with violence and noise" is from 1660s. Sense of "a rapid increase or development" is first attested 1953.
explosive (adj.): 1660s, "tending to explode," from Latin explos-, past participle stem of explodere "drive out, reject" (see explosion) + -ive. As a noun, from 1874. Related: Explosives (n.); explosively; explosiveness.
exponent (n.): 1706, from Latin exponentem (nominative exponens), present participle of exponere "put forth" (see expound). Earliest use is the mathematical one (said to have been introduced in algebra by Descartes) for the symbol to indicate by what power the base number is to be raised. The sense of "one who expounds" is 1812. As an adjective, from 1580s.
exponential (adj.): 1704, from exponent + -ial. As a noun, from 1784. Related: Exponentially.
export (v.): by 1610s, "carrying out of a place;" perhaps from late 15c., from Latin exportare "to carry out, bring out; send away, export," from ex- "away" (see ex-) + portare "carry" (see port (n.1)). The sense of "send out (commodities) from one country to another" is first recorded in English 1660s. Related: Exported; exporting; exporter.
export (n.): 1680s, from export (v.).
expose (v.): early 15c., "to leave without shelter or defense," from Old French esposer, exposer "lay open, set forth, speak one's mind, explain" (13c.), from Latin exponere "set forth, lay open, exhibit, reveal, publish" (see expound), altered by confusion with poser "to place, lay down" (see pose (v.1)). Meaning "to exhibit openly" is from 1620s; that of "to unmask" is from 1690s. Photographic sense is from 1839. Related: Exposed; exposes; exposing.
expose (n.): also exposé, "display of discreditable information," 1803, initially as a French word; noun use of past participle of French exposer "lay open" (see expose (v.)). Earliest use was in reference to Napoleon.
exposition (n.): late 14c., "explanation, narration," from Old French esposicion "explanation, interpretation" (12c.), from Latin expositionem (nominative expositio) "a setting or showing forth; narration, explanation," noun of action from past participle stem of exponere "put forth; explain; expose" (see expound).

The meaning "public display" is first recorded 1851 in reference to the Crystal Palace Exposition in London. Abbreviation Expo is first recorded 1963, in reference to planning for the world's fair held in Montreal in 1967.
expository (adj.): 1620s, from Medieval Latin expositorius, from exposit-, past participle stem of Latin exponere "set forth" (see expound). Earlier in English as a noun meaning "an expository treatise, commentary" (early 15c.). Related: Expositorial.
expostulate (v.): 1530s, "to demand, to claim," from Latin expostulatus, past participle of expostulare "to demand urgently, remonstrate, find fault, dispute, complain of, demand the reason (for someone's conduct)," from ex- "from" (see ex-) + postulare "to demand" (see postulate (v.)). Friendlier sense of "to reason earnestly (with someone) against a course of action, etc." is first recorded in English 1570s. Related: Expostulated; expostulating.
expostulation (n.): 1580s, "action of remonstrating in a friendly manner;" 1590s, "argumentative protest," from Latin expostulationem (nominative expostulatio) "a pressing demand, complaint," noun of action from past participle stem of expostulare "demand urgently" (see expostulate).
exposure (n.): c. 1600, "public exhibition," from expose (v.) + -ure. Sense of "situation with regard to sun or weather" is from 1660s. Photographic sense "act of exposing to light" is from 1839. Indecent exposure attested by 1825.
expound (v.): c. 1300, from Old French espondre "expound (on), set forth, explain," from Latin exponere "put forth, expose, exhibit; set on shore, disembark; offer, leave exposed, reveal, publish," from ex- "forth" (see ex-) + ponere "to put, place" (see position (n.)); with intrusive -d developing in French (compare sound (n.1)); the usual Middle English form was expoune. Related: Expounded; expounding.
'In Englissh,' quod Pacience, 'it is wel hard, wel to expounen, ac somdeel I shal seyen it, by so thow understonde.' ["Piers Plowman," late 14c.]
express (v.1): late 14c., "represent in visual arts; put into words," from Old French espresser, expresser "press, squeeze out; speak one's mind" (Modern French exprimer), Medieval Latin expressare, frequentative of Latin exprimere "represent, describe, portray, imitate, translate," literally "to press out" (source also of Italian espresso); the sense evolution here perhaps is via an intermediary sense such as "clay, etc., that under pressure takes the form of an image," from ex- "out" (see ex-) + pressare "to press, push," from Latin premere (see press (v.1)). Related: Expressed; expresses; expressing; expressible.
express (adj.): late 14c., "stated explicitly, not implied, clearly made known" from Old French espres, expres (13c.), from Latin expressus "clearly presented, distinct, articulated precisely," past participle of exprimere (see express (v.)). Also late 14c. as an adverb, "specially, on purpose;" it also doubled as an adverb in Old French. An express train (1841) originally was one that ran to a certain station.
express (v.2): "to send by express service," 1716, from express (n.).
express (n.): 1610s, "special messenger," from express (adj.). Sense of "business or system for sending money or parcels" is by 1794.
expression (n.): early 15c., "action of pressing out;" later "action of manifesting a feeling" (mid-15c.); "a putting into words" (late 15c.); from Middle French expression (14c.), from Late Latin expressionem (nominative expressio) "expression, vividness," in classical Latin "a pressing out, a projection," noun of action from past participle stem of exprimere "represent, describe," literally "press out" (see express (v.)). Meaning "an action or creation that expresses feelings" is from 1620s. Of the face, from 1774. Occasionally the word also was used literally, for "the action of squeezing out." Related: Expressional.
expressionist (adj.): 1850 in reference to an artist who seeks to portray the emotional experience of the subject, from expression (which was used in the fine arts by 1715 with a sense "way of expressing") + -ist. Modern sense is from 1914, from expressionism (from 1908 as an artistic style or movement). As a noun from 1880. Related: Expressionistic.
expressionless (adj.): 1831, "giving no expression," from expression + -less. Shelley used it with a sense of "unexpressed" (1819).
expressive (adj.): c. 1400, "tending to press out," from French expressif, from expres "clear, plain," from stem of Latin exprimere "to press out," also "to represent, describe" (see express (v.)). Meaning "full of expression" is from 1680s. Related: Expressively; expressiveness.
expressly (adv.): late 14c., "in detail, plainly," from express (adj.) + -ly (2). Meaning "for the express purpose" is c. 1600.