Tree thicket (5)
I believe the answer is:
copse
'tree thicket' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for copse that I've seen before include "Dense growth of shrubs or trees" , "Small group of trees" , "Small thicket" , "Coppice" , "Dense growth of bushes or trees" .)