eg Goldilocks’s bears, roof of dwelling concealed by forest (9)
I believe the answer is:
threesome
'forest' is the definition.
The definition and answer can be both groups as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
I don't understand how the remainder of the clue works.
(Other definitions for threesome that I've seen before include "Magi" , "triplets, perhaps?" , "Horse meet (anag.)" , "triangular event" , "Triad" .)