lichen

Definitions

General English

General Science

  • noun a complex of two organisms growing in symbiosis, a fungus providing the outer shell and an alga or a cyanobacterium giving the organism its colour. Lichens are often found on the surface of stones or trunks of trees.

Medical

  • noun a type of skin disease with thick skin and small lesions
http://www.dictionarycentral.com/definition/lichen.html