lichen has definitions from the fields of botany,medicine
1
[ noun ] (medicine) any of several eruptive skin diseases characterized by hard thick lesions grouped together and resembling lichens growing on rocks

Related terms

skin_disease lichen_planus

2
[ noun ] (botany) any thallophytic plant of the division Lichenes; occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.
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