"Here we go a-wassailing among the leaves so green!" If you've ever heard a caroler sing this phrase and thought, "What the heck is a wassail?", you're not alone!
From the carol, "Here We Come A-wassailing," a wassail is "a toast made to wish good health." And so, in this carol, they seem to be toasting good health quite a lot. More specifically though, this is an Old English toast, adopted from the Old Norse ves heill meaning "be healthy!"