wassailyoudaoicibaDictYouDict[wassail 词源字典]
wassail: [13] Wassail was borrowed from Old Norse ves heill, literally ‘be healthy’. This was a toast or salutation given when about to drink (much like English good health!). Ves was the imperative singular of vesa or vera ‘be’ (a relative of English was and were) and heill is essentially the same word as English hale and whole, and related to healthy.
=> hale, healthy, whole[wassail etymology, wassail origin, 英语词源]
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.