'forest-covered' is a modern English compound formed from 'forest' and the past-participle adjective 'covered'. 'Forest' comes into English via Old French 'forest' (from Medieval Latin 'foresta'), where the root meant 'wood' or 'forest'; 'cover' (past participle 'covered') comes via Old French 'covrir' from Latin 'cooperire', where the root meant 'to cover or overlay'.

'forest' entered English from Old French 'forest' (from Medieval Latin 'foresta'); 'cover' entered from Old French 'covrir' (from Latin 'cooperire'). The compound adjective was created in Modern English by combining the noun 'forest' with the participial form of 'cover' ('-ed') to describe something having a covering of woods.

Individually, 'forest' originally meant 'a wood' and 'cover' 'to overlay'; combined as 'forest-covered' it has long meant 'covered by forest' and has retained that descriptive sense into modern usage.