lichens

Noun

lichen (countable and uncountable, plural lichens or lichen)

1. Any of many symbiotic organisms, being associations of algae and fungi, often found as white or yellow-to-blue–green patches on rocks, old walls, etc.
   • The Beaches of Lukannon–the winter wheat so tall, / The dripping, crinkled lichens, and the sea-fog drenching all!1894 May, Rudyard Kipling, “Lukannon”, in The Jungle Book, London; New York, N.Y.: Macmillan and Co., published June 1894, →OCLC, page 122
2. (figuratively) Something which gradually spreads across something else, causing damage.
   • Meanwhile, abiding a day of judgment, she fought ceaselessly to deny the bitter drops in her cup, to tear back the slow, the intangibly slow growth of a hot, corrosive lichen eating into her heart.1912 January, Zane Grey, “Shadows on the Sage-slope”, in Riders of the Purple Sage […], New York, N.Y.; London: Harper & Brothers Publishers, →OCLC, page 202

   Synonyms:

   cancer

See all 3 meanings of lichen