Pin back a vine (5)
I believe the answer is:
liana
'vine' is the definition.
(liana is a kind of vine)
'pin back a' is the wordplay.
'pin' becomes 'nail' (I've seen this before).
'back' shows that the letters should be reversed in order.
'nail' reversed gives 'lian'.
'lian'+'a'='LIANA'
(Other definitions for liana that I've seen before include "Woody climbing tropical plant -- a nail (anag)" , "Rainforest climber" , "Tropical forest climber" , "Climbing-plant" , "Woody forest climber" .)