Chicken with monkey (4)
I believe the answer is:
wimp
'chicken' is the definition.
(I know that chicken can be written as wimp)
'with monkey' is the wordplay.
'with' becomes 'w' (short for with).
'monkey' becomes 'imp' (synonyms).
'w'+'imp'='WIMP'
(Other definitions for wimp that I've seen before include "Mummy's boy" , "Weak cowardly person" , "Spineless type" , "Milksop" , "A weak ineffectual man" .)