Online Etymology Dictionary

assail (v.): c. 1200, from Old French assalir "attack, assault, assail" (12c., Modern French assaillir), from Vulgar Latin *adsalire "to leap at," from Latin ad- "at" (see ad-) + salire "to leap" (see salient (adj.)). Figurative use from mid-14c. Related: Assailed; assailing; assailable.
assailant (n.): 1530s, from French assailant, noun use of present participle of assailir (see assail). Earlier in same sense was assailer (c. 1400).
assassin (n.): 1530s (in Anglo-Latin from mid-13c.), via French and Italian, from Arabic hashishiyyin "hashish-users," plural of hashishiyy, from the source of hashish (q.v.). A fanatical Ismaili Muslim sect of the time of the Crusades, under leadership of the "Old Man of the Mountains" (translates Arabic shaik-al-jibal, name applied to Hasan ibu-al-Sabbah), with a reputation for murdering opposing leaders after intoxicating themselves by eating hashish. The plural suffix -in was mistaken in Europe for part of the word (compare Bedouin).
assassinate (v.): 1610s, from past participle stem of Medieval Latin assassinare (see assassin). "Assassinate means to kill wrongfully by surprise, suddenly, or by secret assault" [Century Dictionary]. Of reputations, characters, etc., from 1620s. Related: Assassinated; assassinating.
assassination (n.): c. 1600, noun of action from assassinate (v.).
assault (n.): late 14c., earlier asaut (c. 1200), from Old French asaut, assaut "an attack, an assault, attacking forces" (12c.), from Vulgar Latin *adsaltus "attack, assault," from ad "to" (see ad-) + Latin saltus "a leap," from salire "to leap, spring" (see assail). In law by 1580s; historically, assault includes menacing words or actions; battery is an actual blow.
assault (v.): early 15c., from Middle French asauter, assauter, from Vulgar Latin *assaltare (see assault (n.)). Related: Assaulted; assaulting.
assay (v.): c. 1300, "to try, endeavor, strive; test the quality of," from Anglo-French assaier, from assai (n.), from Old French essai "trial" (see essay).
assay (n.): "trial, test of quality, test of character," mid-14c., from Anglo-French assai (see assay (v.)). Meaning "analysis" is from late 14c.
assemblage (n.): c. 1704, from French assemblage "gathering, assemblage," from assembler (see assemble). Earlier English words in the same sense include assemblement, assemblance (both late 15c.).
assemble (v.): early 14c., transitive and intransitive, from Old French assembler "come together, join, unite; gather" (11c.), from Latin assimulare "to make like, liken, compare; copy, imitate; feign, pretend," later "to gather together," from ad- "to" (see ad-) + simulare "to make like" (see simulation). In Middle English and in Old French it also was a euphemism for "to couple sexually." Meaning "to put parts together" in manufacturing is from 1852. Related: Assembled; assembling. Assemble together is redundant.
assembly (n.): c. 1300, "a gathering of persons, a group gathered for some purpose," from Old French as(s)emblee "assembly, gathering; union, marriage," noun use of fem. past participle of assembler "to assemble" (see assemble). Meaning "gathering together" is recorded from early 15c.; that of "act of assembling parts or objects" is from 1914, as is assembly line. School sense is recorded from 1932.
assent (v.): c. 1300, from Old French assentir "agree; get used to" (12c.), from Latin assentare "to agree with," frequentative of assentire, from ad- "to" (see ad-) + sentire "to feel, think" (see sense (n.)). Related: Assented; assenting.
assent (n.): early 14c., "consent, approval," from Old French assent, a back-formation from assentir (see assent (v.)).
assert (v.): c. 1600, "declare," from Latin assertus, past participle of asserere "claim, maintain, affirm" (see assertion). Related: Asserted; asserting. To assert oneself "stand up for one's rights" is recorded from 1879.
assertion (n.): early 15c., assercioun, from Middle French assertion (14c.) or directly from Late Latin assertionem (nominative assertio), noun of action from past participle stem of Latin asserere "claim rights over something, state, maintain, affirm," from ad- "to" (see ad-) + serere "join" (see series). By "joining oneself" to a particular view, one "claimed" or "maintained" it.
assertive (adj.): 1560s, "declaratory, positive, full of assertion," from assert + -ive. Meaning "insisting on one's rights" is short for self-assertive (1865).
assertively (adv.): mid-15c., assertiveli; see assertive + -ly (2).
assertiveness (n.): "tendency toward self-assertion," 1881, from assertive + -ness.
assess (v.): early 15c., "to fix the amount (of a tax, fine, etc.)," from Anglo-French assesser, from Medieval Latin assessare "fix a tax upon," originally frequentative of Latin assessus "a sitting by," past participle of assidere "to sit beside" (and thus to assist in the office of a judge), from ad- "to" (see ad-) + sedere "to sit" (see sedentary). One of the judge's assistant's jobs was to fix the amount of a fine or tax. Meaning "to estimate the value of property for the purpose of taxing it" is from 1809; transferred sense of "to judge the value of a person, idea, etc." is from 1934. Related: Assessed; assessing.
assessable (adj.): mid-15c., from assess + -able.
assessment (n.): 1540s, "value of property for tax purposes," from assess + -ment. Meaning "determination or adjustment of tax rate" is from 1540s; general sense of "estimation" is recorded from 1620s. In education jargon from 1956.
assessor (n.): late 14c., from Old French assessor "assistant judge, assessor (in court)" (12c., Modern French assesseur) and directly from Latin assessor "an assistant, aid; an assistant judge," in Late Latin "one who assesses taxes," literally "a sitter-by," agent noun from past participle stem of assidere "to sit beside" (see assess).
asset (n.): see assets.
assets (n.): 1530s, "sufficient estate," from Anglo-French asetz (singular), from Old French assez (11c.) "sufficiency, satisfaction; compensation," noun use of adverb meaning "enough, sufficiently; very much, a great deal," from Vulgar Latin *ad satis "to sufficiency," from Latin ad- "to" (see ad-) + satis "enough" (see sad).

Beginning as a legal term, "sufficient estate" (to satisfy debts and legacies), it passed into general use; meaning "any property that theoretically can be converted to ready money" is from 1580s. Asset is a 19c. artificial singular. Asset stripping attested from 1972.
asseverate (v.): 1791, from Latin asseveratus, past participle of asseverare "to affirm, insist on, maintain," from ad- "to" (see ad-) + severus "serious, severe" (see severe). Related: Asseverated; asseverating.
asseveration (n.): 1550s, from Latin asseverationem (nominative asseveratio) "vehement assertion, protestation," noun of action from past participle stem of asseverare (see asseverate).
asshole (n.): variant of arsehole (also see ass (n.2)). Meaning "contemptible person," mid-1930s.
assiduity (n.): early 15c., from Latin assiduatem "continual presence," noun of quality from past participle stem of assiduus (see assiduous).
assiduous (adj.): 1530s, from Latin assiduus "attending; continually present, incessant; busy; constant," from assidere "to sit down to" (thus "be constantly occupied" at one's work); from ad "to" (see ad-) + sedere "to sit" (see sedentary). The word acquired a taint of "servility" in 18c. Related: Assiduously; assiduousness.
assiento (n.): 1714, "contract between the King of Spain and another power" (especially that made at the Peace of Utrecht, 1713, with Great Britain for furnishing African slaves to the Spanish colonies in the Americas), from Spanish asiento, from asentar "to adjust, settle, establish," literally "to place on a chair," from a sentar, from Latin sedens, present participle of sedere "to sit" (see sedentary).
assign (v.): c. 1300, from Old French assiginer (13c.) "assign, set (a date, etc.); appoint legally; allot," from Latin assignare "to mark out, to allot by sign, assign, award," from ad- "to" (see ad-) + signare "make a sign," from signum "mark" (see sign). Main original use was in English law, in transferences of personal property. General meaning "to fix, settle, determine, appoint" is from c. 1300. Related: Assigned; assigning.
assignation (n.): early 14c., "appointment by authority," from Old French assignacion (14c., Modern French assignation), from Latin assignationem (nominative assignatio) "an assigning, allotment," noun of action from past participle stem of assignare (see assign). Meaning "action of legally transfering" (a right or property) is from 1570s; that of "a meeting by arrangement, tryst" is from 1650s.
assignee (n.): early 15c., "one who is appointed to act for another," from Old French assigne, past participle of assignier (see assign).
assignment (n.): late 14c., "order, request, directive," from Old French assignement "(legal) assignment (of dower, etc.)," from Late Latin assignamentum, noun of action from Latin assignare (see assign). Meaning "appointment to office" is mid-15c.; that of "a task assigned" (to someone) is from c. 1848.
assimilate (v.): early 15c., from Latin assimilatus "feigned, pretended, fictitious," past participle of assimilare "to make like," from ad- "to" (see ad-) + simulare "make similar," from similis "like, resembling" (see similar). Originally transitive (with to); intransitive use first recorded 1837. Related: Assimilated; assimilating.
assimilation (n.): early 15c., "act of assimilating," from Old French assimilacion, from Latin assimilationem (nominative assimilatio) "likeness, similarity," noun of action from past participle stem of assimilare (see assimilate). Psychological sense is from 1855.
assimilationist (n.): "one who advocates racial or ethnic integration," 1900, in reference to possible U.S. attitudes toward Hawaii and possessions obtained in the war against Spain; usually with reference to Jews in European nations; see assimilation + -ist.
assist (v.): early 15c., from Middle French assister "to stand by, help, put, place, assist" (14c.), from Latin assistere "stand by, take a stand near, attend," from ad- "to" (see ad-) + sistere "stand still, take a stand; to set, place, cause to stand," from PIE *si-st-, reduplicated form of root *stā- "to stand" (see stet). Related: Assisted; assisting. Medical assisted suicide attested from 1884.
assist (n.): 1570s, "an act of assistance," from assist (v.). In the sporting sense attested 1877 in baseball, 1925 in ice hockey.
assistance (n.): early 15c., "act of helping or aiding," from Middle French assistance, from assister (see assist (v.)).
assistant (n.): mid-15c., assistent "one who helps or aids another," from Middle French assistent, adjective and noun, properly present participle of assister (see assist (v.)).
assistant (adj.): mid-15c., "helpful, of assistance," from Middle French assistent (see assistant (n.)).
assize (n.): "session of a law court," c. 1300 (attested from mid-12c. in Anglo-Latin), from Old French assise "session, sitting of a court" (12c.), properly fem. past participle of asseoir "to cause to sit," from Latin assidere "to sit beside" (see assess). Originally "all legal proceedings of the nature of inquests or recognitions;" hence sessions held periodically in each county of England to administer civil and criminal justice.
associate (v.): mid-15c., from Latin associatus past participle of associare "join with," from ad- "to" (see ad-) + sociare "unite with," from socius "companion" (see social (adj.)). Related: Associated; associating. Earlier form of the verb was associen (late 14c.), from Old French associier "associate (with)."
associate (n.): 1530s, from associate (adj.).
associate (adj.): early 15c., "allied, connected, paired," from Latin associatus, past participle of associare (see associate (v.)).
association (n.): 1530s, "action of coming together," from Medieval Latin associationem (nominative associatio), noun of action from past participle stem of associare (see associate). Meaning "a body of persons with a common purpose" is from 1650s. Meaning "mental connection" is from 1680s; that of "quality or thing called to mind by something else" is from 1810.
associative (adj.): 1812, from associate (v.) + -ive.
assonance (n.): 1727, "resemblance of sounds between words," from French assonance, from assonant, from Latin assonantem (nominative assonans), present participle of assonare "to resound, respond to," from ad- "to" (see ad-) + sonare "to sound" (see sonata). Properly, in prosody, "rhyming of accented vowels, but not consonants" (1823).