英语词源字典 - 在线词源网站

undecennial (adj.)[undecennial 词源字典]: "occurring every 11 years," 1858, in reference to solar activity cycle, from Latin undecim "eleven" + ending from biennial, etc.[undecennial etymology, undecennial origin, 英语词源]
undecided (adj.): 1530s, "not decided, unsettled," from un- (1) "not" + past participle of decide (v.).
undecipherable (adj.): 1758, from un- (1) "not" + decipherable (see decipher (v.)).
undecisive (adj.): 1660s, from un- (1) "not" + decisive. The usual word is indecisive.
undefeated (adj.): 1701, from un- (1) "not" + past participle of defeat (v.).
undefended (adj.): 1560s, "not defended, unprotected," from un- (1) "not" + past participle of defend (v.). Attested earlier in a now-obsolete sense of "unforbidden" (late 14c.).
undefiled (adj.): c. 1300, undefylde, from un- (1) "not" + past participle of defile (v.). Originally of morals; sexual sense is attested from mid-15c. Physical sense of "not made dirty" is from 1580s.
undefined (adj.): 1610s, from un- (1) "not" + past participle of define (v.).
undelivered (adj.): late 15c., from un- (1) "not" + past participle of deliver (v.).
undemanding (adj.): 1879, from un- (1) "not" + demanding (adj.).
undemonstrative (adj.): 1826, "not characterized by outward expression of feelings," from un- (1) "not" + demonstrative (adj.).
undeniable (adj.): 1540s, from un- (1) "not" + deny + -able. In 19c., often with a sense of "undeniably good." Related: Undeniably.
under (prep., adv.): Old English under (prep.) "beneath, among, before, in the presence of, in subjection to, under the rule of, by means of," also, as an adverb, "beneath, below, underneath," expressing position with reference to that which is above, from Proto-Germanic *under- (cognates: Old Frisian under, Dutch onder, Old High German untar, German unter, Old Norse undir, Gothic undar), from PIE *ndher- "under" (cognates: Sanskrit adhah "below;" Avestan athara- "lower;" Latin infernus "lower," infra "below").

Productive as a prefix in Old English, as in German and Scandinavian (often forming words modeled on Latin ones in sub-). Notion of "inferior in rank, position, etc." was present in Old English. With reference to standards, "less than in age, price, value," etc., late 14c. As an adjective, "lower in position; lower in rank or degree" from 13c. Also used in Old English as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand).

Under the weather "indisposed" is from 1810. Under the table is from 1921 in the sense of "very drunk," 1940s in sense of "illegal." To get something under (one's) belt is from 1954; to keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1540s; to speak under (one's) breath "in a low voice" is attested from 1832. To be under (someone's) thumb "entirely controlled" (by that person) is recorded from 1754.
under-achiever (n.): also underachiever, 1953, from under + agent noun from achieve (v.). Under-achievement is recorded from 1951.
under-employed (adj.): 1908, "not used to optimum capacity," originally in reference to working persons, from under + past participle of employ (v.).
under-employment (n.): also underemployment, 1909, from under + employment.
underage (adj.): also under-age, 1590s, from under + age (n.).
underarm (adj.): 1816, "underhand" (in reference to a style of throwing), from under + arm (n.1). First attested 1908 in dressmaking sense of "seams on the lower half of the arm-hole;" as a euphemism for armpit, it is attested from 1930s, popularized by advertisers.
underbelly (n.): c. 1600, from under + belly (n.). In figurative sense of "most vulnerable part" it is recorded from Churchill's 1942 speech. Sometimes used erroneously or euphemistically in sense of "seamy or sordid part" of anything.
underbid (v.): 1610s, from under + bid (v.). Related: Underbidding.