eveningyoudaoicibaDictYouDict[evening 词源字典]
evening: [OE] Evening is a derivative of even [OE], a word for ‘evening’ now restricted to bad poetry. This came ultimately from an Indo- European base, whose general meaning of ‘lateness’ is pointed up by other descendants such as Sanskrit apara- ‘later, western’, Greek opsé ‘late’, and Gothic iftuma ‘following, later’. The specific application to ‘latter part of the day’ seems only to have occurred in the Germanic languages, where it is represented in German abend and Dutch avond, and also possibly in Swedish afton and Danish aften (although these could be from another source).

The Old English word was ǣfen, which formed the basis of a verb ǣfnian ‘become evening’; the verbal noun derived from this has become English evening. Eve [13], as in ‘Christmas eve’, is a Middle English reduction of even.
[evening etymology, evening origin, 英语词源]
Christmas (n.)youdaoicibaDictYouDict
late Old English Cristes mæsse, from Christ (and retaining the original vowel sound) + mass (n.2).

Written as one word from mid-14c. As a verb from 1590s. Father Christmas first attested in a carol attributed to Richard Smart, Rector of Plymtree (Devon) from 1435-77. Christmas tree in modern sense first attested 1835 in American English, from German Weihnachtsbaum. Christmas cards first designed 1843, popular by 1860s. Christmas Eve is Middle English Cristenmesse Even (c. 1300).
wassailyoudaoicibaDictYouDict
mid-12c., from Old Norse ves heill "be healthy," a salutation, from ves, imperative of vesa "to be" (see was) + heill "healthy," from Proto-Germanic *haila- (see health). Use as a drinking phrase appears to have arisen among Danes in England and spread to native inhabitants.

A similar formation appears in Old English wes þu hal, but this is not recorded as a drinking salutation. Sense extended c. 1300 to "liquor in which healths were drunk," especially spiced ale used in Christmas Eve celebrations. Meaning "a carousal, reveling" first attested c. 1600. Wassailing "custom of going caroling house to house at Christmas time" is recorded from 1742.