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[lahy-kuh n] /ˈlaɪ kən/
any complex organism of the group Lichenes, composed of a fungus in symbiotic union with an alga and having a greenish, gray, yellow, brown, or blackish thallus that grows in leaflike, crustlike, or branching forms on rocks, trees, etc.
Pathology. any of various eruptive skin diseases.
verb (used with object)
to cover with or as if with lichens.
Origin of lichen
1595-1605; < Latin līchēn < Greek leichḗn
Related forms
lichenization, noun
lichenlike, adjective
unlichened, adjective
Can be confused
lichen, liken. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for lichen


/ˈlaɪkən; ˈlɪtʃən/
an organism that is formed by the symbiotic association of a fungus and an alga or cyanobacterium and occurs as crusty patches or bushy growths on tree trunks, bare ground, etc. Lichens are now classified as a phylum of fungi (Mycophycophyta)
(pathol) any of various eruptive disorders of the skin
Derived Forms
lichened, adjective
lichen-like, adjective
lichenoid, adjective
lichenous, lichenose, adjective
Word Origin
C17: via Latin from Greek leikhēn, from leikhein to lick
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for lichen

c.1600, from Latin lichen, from Greek leichen, originally "what eats around itself," probably from leichein "to lick" (see lick). Originally used of liverwort; the modern sense first recorded 1715. Related: Lichenaceous.

Online Etymology Dictionary, © 2010 Douglas Harper
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lichen in Medicine

lichen li·chen (lī'kən)
Any of various skin diseases characterized by patchy eruptions of small, firm papules.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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lichen in Science
The mutualistic symbiotic association of a fungus with an alga or a cyanobacterium, or both. The fungal component of a lichen absorbs water and nutrients from the surroundings and provides a suitable environment for the alga or cyanobacterium. These live protected among the dense fungal hyphae and produce carbohydrates for the fungus by photosynthesis. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. The more familiar lichens grow slowly as crusty patches, but lichens are found in a variety of forms, such as the tall, plantlike reindeer moss. The association between the different organisms in a lichen is so close that lichens are routinely referred to as a single organism, and scientists classify lichens using the name of the fungal component.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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