Fine antique pen (4)
I believe the answer is:
fold
'pen' is the definition.
(fold is a kind of pen)
'fine antique' is the wordplay.
'fine' becomes 'f' (abbreviation).
'antique' becomes 'old' ('old' can be similar in meaning to 'antique').
'f'+'old'='FOLD'
(Other definitions for fold that I've seen before include "Tuck - pen" , "Gather < church" , "go bankrupt, perhaps" , "close" , "Church following" .)