c.1140, from O.N.
ves heill "be healthy," a salutation, from
ves, imperative of
vesa "to be" (see
was) +
heill "healthy" (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 O.E.
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 1602.
Wassailing "custom of going caroling house to house at Christmas time" is recorded from 1742.