Bitterness linked to long time in ship (7)
I believe the answer is:
galleon
'ship' is the definition.
(I've seen this before)
'bitterness linked to long time' is the wordplay.
'bitterness' becomes 'gall' ('gall' can be a synonym of 'bitterness').
'linked to' is a charade indicator (letters next to each other).
'long time' becomes 'eon' (eon is a kind of long time).
'gall'+'eon'='GALLEON'
'in' is the link.
(Other definitions for galleon that I've seen before include "Ship of the line" , "Large Spanish sailing ship of yore" , "All gone (anag.)" , "Large old square-rigged sailing ship" , "Large old sailing vessel" .)