lichen (n.) Look up lichen at
1715, from Latin lichen, from Greek leichen "tree-moss, lichen," originally "what eats around itself," probably from leichein "to lick" (see lick (v.1)). 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.