Cork perhaps from sun hat (7)
I believe the answer is:
stopper
'cork perhaps' is the definition.
(cork is a kind of stopper)
'sun hat' is the wordplay.
'sun' becomes 's'.
'hat' becomes 'topper' (topper is a kind of hat).
's'+'topper'='STOPPER'
'from' acts as a link.
(Other definitions for stopper that I've seen before include "Perhaps cork" , "One who checks" , "Plug for a bottle" , "Bung" , "Cork - goalkeeper?" .)