lichen n.

1715, from Latin lichen, from Greek leichen "tree-moss, lichen," originally "what eats around itself," probably from leichein "to lick" (from PIE root *leigh- "to lick"). Used earlier (c. 1600) of liverwort, which was thought to be related. Also in English, as in Greek, of eczema and certain other skin diseases. Related: Lichenic; licheniform; lichenous; lichenaceous.