Fish or beef (4)
I believe the answer is:
carp
I believe this clue is a double definition.
'fish' is the first definition.
(carp is a kind of fish)
'beef' is the second definition.
(I've seen this before)
'or' acts as a link.
(Other definitions for carp that I've seen before include "Pond fish" , "ish" , "Fish - grouse" , "Continually nag; fish" , "Nagging fish?" .)