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

Away from the shore, the tundra is barren, a broad expanse of moss, lichen, and exposed rock. — Joshua Yaffa, New Yorker, 2 Nov. 2026

Anyone can develop lichen sclerosus, but postmenopausal women face the highest risk. — Emily Cegielski, Flow Space, 20 Oct. 2026

For alopecia areata or scarring hair loss conditions such as lichen planopilaris, frontal fibrosing alopecia and central centrifugal cicatricial alopecia, treating inflammation is key. — Hanna Wickes, Miami Herald, 7 Oct. 2026

Over time, these rocks are fragmented and broken up into small mineral particles by plant roots forcing open cracks, or lichens secreting chemicals that dissolve rocks to release nutrients. — Literary Hub, 2 Oct. 2026

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)