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

Was this blemish somewhat new, or had it, like the rest of the decay in her life—the age spots that bloomed like lichen across the top of her hands, the foreshortening plait of her spine—been stealthily creeping up on her? —Literary Hub, 9 July 2025

The key to determining which planets could host extraterrestrial life could be growing in the harshest deserts of Earth in the form of lichen. —Robert Lea, Space.com, 26 June 2025

After another few minutes, King pointed out century-old tree trunks covered with lichen, a native witch-hazel bush blooming, its yellow flower a lone mark of color in a still-brown grove. —Robert Sullivan, Curbed, 9 June 2025

In any case, there are sure to be at least a few flecks of moss or lichen, gray or gray-green, on that side. —Ted Updike, Outdoor Life, 22 May 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)