Definition of "lichen" []

• A fungus, usually of the class Ascomycetes, that grows symbiotically with algae, resulting in a composite organism that characteristically forms a crustlike or branching growth on rocks or tree trunks. (noun)
• Pathology Any of various skin diseases characterized by patchy eruptions of small, firm papules. (noun)
• To cover with lichens. (verb-transitive)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "I love old graveyards, especially when the stones are weathered and covered in lichen or ivy."
• "But not before I've admired the extra-large version of your picture, and admired the way the lichen is growing in the bottoms of the incised letters."
• "How could we even consider trusting blokes who look as though the triffid like lichen from the last cave they lived has taken root in their heart?"