1. A composite organism made up of a fungus, usually an ascomycete, that grows symbiotically with an alga or a cyanobacterium and characteristically forms a crustlike or branching growth on rocks or tree trunks.
2. Medicine Any of various skin diseases characterized by patchy eruptions of small, firm papules.
tr.v. li·chened, li·chen·ing, li·chens
To cover with lichens.
[Latin līchēn, a kind of plant, from Greek leikhēn, from leikhein, to lick; see leigh- in the Appendix of Indo-European roots.]
(click for a larger image)lichen
common orange lichen
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.