lichen

noun

li·​chen ˈlī-kən 

 British also  ˈli-chən

1

: any of numerous complex plantlike organisms made up of an alga or a cyanobacterium and a fungus growing in symbiotic association on a solid surface (such as on a rock or the bark of trees)

Note: The main body of the lichen, known as the thallus, is formed by fungal filaments which surround the photosynthetic algal or cyanobacterial cells. The lichen is usually described as having a leaflike (foliose), crusty (crustose), or branching shrub-like (fruticose) form. Lichens often play an important part in the weathering of rocks and include some that are sources of natural dyes.

2

: any of several skin diseases characterized by the eruptions of flat papules

lichened

ˈlī-kənd 

 British also  ˈli-chənd

adjective

lichenous

ˈlī-kə-nəs 

 British also  ˈli-chə-

adjective

Illustration of lichen

• lichen 1

Examples of lichen in a Sentence

Recent Examples on the Web

Extreme weather at the poles stresses crucial moss and lichen, and shreds entire habitats in hours. —Marion Renault, The Atlantic, 29 Sep. 2025

Reindeer moss, used as a mulch for containerized plants, is a fibrous chartreuse lichen grazed by caribou and reindeer in Arctic lands. —Joshua Siskin, Oc Register, 26 Sep. 2025

The freezing rain then traps lichen under a thick layer of ice where hungry reindeer can’t reach the food, according to Anna Skarin, a reindeer husbandry expert and Swedish University of Agricultural Sciences professor. —Jason Ma, Fortune, 7 Sep. 2025

Meanwhile, a steep descent leads to Tappiya Falls—thundering into a jade basin as mist clings to lichen-slick boulders. —Lewis Nunn, Forbes.com, 24 Aug. 2025

Word History

Etymology

Latin, from Greek leichēn, lichēn, from leichein to lick

First Known Use

circa 1657, in the meaning defined at sense 2

Rhymes for lichen

• glycan
• liken
• peptidoglycan
• proteoglycan

Kids Definition

lichen

noun

li·​chen ˈlī-kən 

: any of numerous plantlike living things made up of an alga and a fungus growing together on a solid surface (as a rock or a tree)

Medical Definition

lichen

noun

li·​chen ˈlī-kən 

1

: any of several skin diseases characterized by the eruption of flat papules

especially : lichen planus

2

: any of numerous complex plantlike organisms made up of an alga and a fungus growing in symbiotic association on a solid surface (as a rock)