名詞 lichen:

1. any of several eruptive skin diseases characterized by hard thick lesions grouped together and resembling lichens growing on rocks
2. any thallophytic plant of the division Lichenes; occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.

1. The rock is full of lichen.
   巖石上長滿了青苔。

li.chen

n.（名詞）
A fungus, usually of the class Ascomycetes, that grows symbiotically with algae, resulting in a composite organism that characteristically forms a crustlike or branching growth on rocks or tree trunks.
地衣：一種真菌類植物，通常屬于子囊菌綱，與藻共生形成一種復合有機體，生長于巖石或樹干上，多為硬殼狀或枝叉狀
Pathology Any of various skin diseases characterized by patchy eruptions of small, firm papules.
【病理學】 苔蘚?。阂环N皮膚病，以出現斑狀的小而硬的丘疹為特征
v.tr.（及物動詞）
li.chened,li.chen.ing,li.chens
To cover with lichens.
用地衣覆蓋

來源：
Latin lochôn [a kind of plant]
拉丁語 lochôn [一種植物]
from Greek leikhôn
源自 希臘語 leikhôn
from leikhein [to lick] * see leigh-
源自 leikhein [舔] *參見 leigh-

【引伸】
li.chenous
adj.（形容詞）