Fighting to slice fish or chicken (6)
I believe the answer is:
coward
'chicken' is the definition.
(similar in meaning)
'fighting to slice fish' is the wordplay.
'fighting' becomes 'war'.
'to slice' is an insertion indicator (inserted letters slice their way in).
'fish' becomes 'cod' (type of fish).
'war' put into 'cod' is 'COWARD'.
'or' is the link.
(Other definitions for coward that I've seen before include "Person without courage" , "Someone lacking courage" , "who would shy away from difficulties?" , "Person who is deficient in courage" , "A craven person" .)