Manage to encircle small thicket (5)
I believe the answer is:
copse
'thicket' is the definition.
(synonyms)
'manage to encircle small' is the wordplay.
'manage' becomes 'cope' (synonyms).
'to encircle' means one lot of letters goes inside another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'cope' placed around 's' is 'COPSE'.
(Other definitions for copse that I've seen before include "Small group of trees" , "Coppice" , "Dense growth of shrubs or trees" , "Wood - thicket" , "Harvested woodland" .)