Online Etymology Dictionary

enter (v.): late 13c. entren, "enter into a place or a situation; join a group or society" (trans.); early 14c., "make one's entrance" (intrans.), from Old French entrer "enter, go in; enter upon, assume; initiate," from Latin intrare "to go into, enter" (source of Spanish entrar, Italian entrare), from intra "within," related to inter (prep., adj.) "among, between" (see inter-). Transitive and intransitive in Latin; in French intransitive only. From c. 1300 in English as "join or engage in: (an activity);" late 14c. as "penetrate," also "have sexual intercourse" (with a woman);" also "make an entry in a record or list," also "assume the duties" (of office, etc.). Related: Entered; entering.
enteric (adj.): "pertaining to the intestines," 1822, from Latinized form of Greek enterikos "intestinal," first used in this sense by Aristotle, from entera (plural; singular enteron) "intestines," from PIE *enter-, comparative of *en "in" (see inter-).
enteritis (n.): "acute inflammation of the bowels," 1808, medical Latin, coined c. 1750 by French pathologist François-Boissier de la Croix de Sauvages (1706-1767), from enteron "intestine" (see enteric) + -itis "inflammation."
entero-: before vowels enter-, word-forming element meaning "intestine," from comb. form of Greek enteron "an intestine, piece of gut" (see enteric).
enterovirus (n.): 1957; see entero- + virus.
enterprise (n.): early 15c., "an undertaking," formerly also enterprize, from Old French enterprise "an undertaking," noun use of fem. past participle of entreprendre "undertake, take in hand" (12c.), from entre- "between" (see entre-) + prendre "to take," contraction of prehendere (see prehensile). Abstract sense of "adventurous disposition, readiness to undertake challenges, spirit of daring" is from late 15c.
enterprising (adj.): "eager to undertake, prompt to attempt," 1610s, present participle adjective from the verb enterprise (late 15c.), from the noun enterprise. Until mid-19c. (at least in Britain) mostly in a bad sense: "scheming, ambitious, foolhardy." Earlier (1560s) as a verbal noun meaning "action of undertaking."
entertain (v.): late 15c., "to keep up, maintain, to keep (someone) in a certain frame of mind," from Middle French entretenir, from Old French entretenir "hold together, stick together, support" (12c.), from entre- "among" (from Latin inter; see inter-) + tenir "to hold" (from Latin tenere; see tenet).

Sense of "have a guest" is late 15c.; that of "gratify, amuse" is 1620s. Meaning "to allow (something) to consideration, take into the mind" (of opinions, notions, etc.) is 1610s. Related: Entertained; entertaining.
entertainer (n.): "public performer," 1530s, agent noun from entertain.
entertainment (n.): 1530s, "provision for support of a retainer; manner of social behavior," now obsolete, along with other 16c. senses; from entertain + -ment. Meaning "the amusement of someone" is from 1610s; sense of "that which entertains" is from 1650s; that of "public performance or display meant to amuse" is from 1727.
enthalpy (n.): 1927 in physics, from Greek enthalpein "to warm in," from en "in" (see en- (2)) + thalpein "to heat," from thalpos "warmth, heat," especially "summer heat."
enthrall (v.): also enthral "to hold in mental or moral bondage," 1570s, from en- (1) "make, put in" + thrall (n.). Literal sense (1610s) is rare in English. Related: Enthralled; enthralling.
enthrone (v.): c. 1600, from en- (1) + throne (n.). Replacing enthronize (late 14c.), from Old French introniser (13c.), from Late Latin inthronizare, from Greek enthronizein. Also simply throne (v.), late 14c., from the noun in English. Related: Enthroned; enthroning.
enthuse (v.): 1827, American English, back-formation from enthusiasm. Originally often humorous or with affected ignorance. Related: enthused; enthusing.
enthusiasm (n.): c. 1600, from Middle French enthousiasme (16c.) and directly from Late Latin enthusiasmus, from Greek enthousiasmos "divine inspiration, enthusiasm (produced by certain kinds of music, etc.)," from enthousiazein "be inspired or possessed by a god, be rapt, be in ecstasy," from entheos "divinely inspired, possessed by a god," from en "in" (see en- (2)) + theos "god" (see theo-). Acquired a derogatory sense of "excessive religious emotion through the conceit of special revelation from God" (1650s) under the Puritans; generalized meaning "fervor, zeal" (the main modern sense) is first recorded 1716.
enthusiast (n.): 1560s, pejorative, "one who believes himself possessed of divine revelations or special communication from God," from Greek enthousiastes "a person inspired," from enthousiazein (see enthusiasm). General sense (not always entirely pejorative) is from mid-18c.
enthusiastic (adj.): c. 1600, "pertaining to possession by a deity," from Greek enthousiastikos "inspired," from enthousiazein "be possessed or inspired by a god" (see enthusiasm). Meaning "pertaining to irrational delusion in religion" is from 1690s. The main modern sense, in reference to feelings or persons, "intensely eager, rapturous," is from 1786. Related: Enthusiastically.
enthymeme (n.): "a syllogism in which one premise is omitted," in Aristotle, "an inference from likelihoods and signs," 1580s, from Latin enthymema, from Greek enthymema "thought, argument, piece of reasoning," from enthymesthai "to think, consider," literally "to keep in mind, take to heart," from en "in" (see en- (2)) + thymos "mind" (see fume (n.)). Related: Enthymematic.
entice (v.): late 13c., intice, from Old French enticier "to stir up (fire), to excite, incite," which is of uncertain origin, perhaps from Vulgar Latin *intitiare "set on fire," from Latin in- "in" (see in- (2)) + titio (genitive titionis) "firebrand," which is of uncertain origin. Meaning "to allure, attract" is from c. 1300. Related: Enticed; enticing; enticingly.
enticement (n.): c. 1300, "thing which entices," from Old French enticement "incitement, instigation, suggestion," from enticier (see entice). From 1540s as "action of enticing."
entire (adj.): late 14c., from Old French entier "whole, unbroken, intact, complete," from Latin integrum "completeness" (nominative integer; see integer). Related: Entireness.
entirely (adv.): mid-14c., from entire + -ly (2).
entirety (n.): also entierty, mid-14c., enterete, intierty, from Anglo-French entiertie, Old French entiereté "totality, entirety; integrity, purity," from Latin integritatem (nominative integritas) "completeness, soundness, integrity," from integer (see integer).
entitle (v.): also intitle, late 14c., "to give a title to a chapter, book, etc.," from Anglo-French entitler, Old French entiteler "entitle, call" (Modern French intituler), from Late Latin intitulare "give a title or name to," from in- "in" (see in- (2)) + titulus "title" (see title (n.)).

Meaning "to bestow (on a person) a rank or office" is mid-15c. Sense of "to give (someone) 'title' to an estate or property," hence to give that person a claim to possession or privilege, is mid-15c.; this now is used mostly in reference to circumstances and actions. Related: Entitled; entitling.
entitlement (n.): 1823, perhaps in some senses from French entitlement, which was in Old French as "tit;e (of a book), inscription," and later was used in legal language; but also in part a native formation from entitle + -ment. Entitlement culture attested by 1994 (culture of entitlement is from 1989).
entity (n.): 1590s, from Late Latin entitatem (nominative entitas), from ens (genitive entis) "a thing," proposed by Caesar as present participle of esse "be" (see is), to render Greek philosophical term to on "that which is" (from neuter of present participle of einai "to be;" see essence). Originally abstract; concrete sense in English is from 1620s.
ento-: word-forming element used chiefly in biology and meaning "within, inside, inner," from Greek ento-, comb. form of entos (adv., prep.) "within, inside," as a noun, "inner parts" (cognate with Latin intus), from PIE *entos-, extended form of root *en "in" (see in), with adverbial suffix *-tos, denoting origin.
entomb (v.): 1570s, from Old French entomber "place in a tomb," from en- "in" (see en- (1)) + tombe "tomb" (see tomb). Related: Entombed; entombing. The earlier verb was simply tomb (c. 1300).
entombment (n.): 1660s, from entomb + -ment.
entomolite (n.): "fossilized insect," 1813, from entomo-, comb. form of Greek entomon "insect" (see entomology) + -lite "stone." Late 18c. in French and German.
entomologist (n.): 1771; see entomology + -ist.
entomology (n.): 1764, from French entomologie (1764), coined from -logie "study of" (see -logy) + Greek entomon "insect," neuter of entomos "cut in pieces, cut up," in this case "having a notch or cut (at the waist)," from en "in" (see en- (2)) + temnein "to cut" (see tome).

Insects were so called by Aristotle in reference to the segmented division of their bodies. Compare insect, which is from a Latin loan-translation of the Greek word. Related: Entomological; entomologically. Hybrid insectology (1766, from French insectologie, 1744) is not much used.
I have given the name insectology to that part of natural history which has insects for its object; that of entomology ... would undoubtedly have been more suitable ... but its barbarous sound terryfy'd me. [Charles Bonnet's English translation of his "Contemplation de la nature," 1766]
entomophagous (adj.): "insectivorous," 1800, from entomo-, comb. form of Greek entomon "insect" (see entomology) + -phagous.
entoparasite (n.): 1847; see ento- + parasite. Perhaps from German or French.
entourage (n.): 1832, "surroundings, environment," picked up by De Quincey from French entourage, from Middle French entourer "to surround" (16c.), from Old French entour "that which surrounds" (10c.), from en- "in" (see en- (1)) + tour "a circuit" (see tour). Specific sense of "attendant persons, persons among whom as followers or companions one is accustomed to move" recorded in English by 1860.
entrails (n.): "internal parts of animal bodies," c. 1300, from Old French entrailles (12c.), from Late Latin intralia "inward parts, intestines" (8c.), from altered form of Latin interanea, noun use of neuter plural of interaneus "internal, that which is within," from inter "between, among" (see inter-). Latin interanea yielded Late Latin intrania, hence Italian entrango, Spanish entrañas, Old French entraigne; the alternative form that led to the Modern English word evidently is from influence of the Latin neuter plural (collective) adjective suffix -alia (French -aille).
entrain (v.1): "to draw along," 1560s, a term in chemistry, from French entrainer (12c.), from en- "away" (see en- (1)) + trainer "to drag" (see train (n.)). Related: Entrained; entrainment.
entrain (v.2): "get on board a locomotive train," 1860s, from en- (1) "in, into" + train (n.). Related: Entrained.
entrammel (v.): "to entangle," 1590s, from en- (1) "in" + trammel (n.).
entrance (n.): 1520s, "act of entering," from Middle French entrance, from entrer (see enter). Sense of "door, gate" first recorded in English 1530s. Meaning "a coming of an actor upon the stage" is from c. 1600.
entrance (v.): "to throw into a trance," 1590s, from en- (1) "put in" + trance (n.). Meaning "to delight" also is 1590s. Related: Entranced; entrancing; entrancement.
entrant (n.): 1630s, "one who enters, a beginner" (of professions, etc.); from French entrant, present participle of entrer (see enter). From 1838 with reference to one who enters a contest. As an adjective from 1630s.
entrap (v.): "to catch, as in a trap," 1530s, intrappe, from Old French entraper "trap, catch in a trap;" see en- (1) + trap (n.). Related: Entrapped; entrapping.
entrapment (n.): 1590s, from entrap + -ment. Criminal investigation sense attested by 1896.
entre nous: "in private," French, literally "between ourselves."
entre-: in words from French, corresponds to English enter-, which is itself from French entre "between, among" (11c.), from Latin inter (see inter-).
entreat (v.): c. 1400, "to enter into negotiations," especially "discuss or arrange peace terms;" also "to treat (someone) in a certain way," from Anglo-French entretier, Old French entraiter "to treat," from en- "make" (see en- (1)) + traiter "to treat" (see treat (v.)). Meaning "to beseech, implore, plead with (someone)" is from early 15c.; meaning "to plead for (someone)" is from mid-15c. Related: Entreated; entreating.
entreaty (n.): mid-15c., "treatment; negotiation;" see entreat + -y (1). Meaning "urgent solicitation, earnest request" is from 1570s. Related: Entreaties.
entree (n.): 1724, "opening piece of an opera or ballet," from French entrée, from Old French entree (see entry). Cookery sense is from 1759; originally the dish which was introductory to the main course. Meaning "entry, freedom of access" is from 1762. The word had been borrowed in Middle English as entre "act of entering."
entrench (v.): also intrench, 1550s, implied in intrenched, from en- (1) "make, put in" + trench (n.). Figurative use is from 1590s. Related: Entrenched; entrenching.