Heather almost trapped deserter, wandering (7)
I believe the answer is:
erratic
'wandering' is the definition.
('erratic' can be a synonym of 'wandering')
'heather almost trapped deserter' is the wordplay.
'heather' becomes 'erica' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'trapped' means one lot of letters goes inside another.
'deserter' becomes 'rat' (I've seen this before).
'erica' with its last letter taken off is 'eric'.
'eric' going around 'rat' is 'ERRATIC'.
(Other definitions for erratic that I've seen before include "Irregular or uneven in movement or habit" , "Irregular, capricious" , "Haphazard" , "Irregular, not dependable" , "Irregular or uneven in movement or habits" .)