evenyoudaoicibaDictYouDict[even 词源字典]
even: [OE] Even can be traced back to a prehistoric Germanic *ebnaz, although it is not clear whether it meant originally ‘flat, level’ or ‘equal, alike’ (both strands of meaning are still present in the word, the latter in such expressions as ‘get even with’ and ‘even number’, and also in its various adverbial uses, the former in ‘even keel’, ‘even light’, etc)
[even etymology, even origin, 英语词源]
even (adj.)youdaoicibaDictYouDict
Old English efen "level," also "equal, like; calm, harmonious; equally; quite, fully; namely," from Proto-Germanic *ebnaz (cognates: Old Saxon eban, Old Frisian even "level, plain, smooth," Dutch even, Old High German eban, German eben, Old Norse jafn, Danish jævn, Gothic ibns). The adverb is Old English efne "exactly, just, likewise." Modern adverbial sense (introducing an extreme case of something more generally implied) seems to have arisen 16c. from use of the word to emphasize identity ("Who, me?" "Even you").

Etymologists are uncertain whether the original sense was "level" or "alike." Used extensively in Old English compounds, with a sense of "fellow, co-" (as in efeneald "of the same age;" Middle English even-sucker "foster-brother"). Of numbers, from 1550s. Sense of "on an equal footing" is from 1630s. Rhyming reduplication phrase even steven is attested from 1866; even break (n.) first recorded 1907. Even-tempered from 1712. To get even with "retaliate upon" is attested by 1833.
even (v.)youdaoicibaDictYouDict
Old English efnan "to make even, to make level; liken, compare" (see even (adj.)). Intransitive sense of "become even" is attested from early 13c. Related: Evened; evening.
even (n.)youdaoicibaDictYouDict
"end of the day," Old English æfen, Mercian efen, Northumbrian efern (see eve).