Substitute carp with eel for cooking (7)
I believe the answer is:
replace
'substitute' is the definition.
(synonyms)
'carp with eel for cooking' is the wordplay.
'with' means one lot of letters go next to another.
'for cooking' is an anagram indicator.
'carp' after 'eel' is 'eelcarp'.
'eelcarp' with letters rearranged gives 'REPLACE'.
(Other definitions for replace that I've seen before include "Provide a substitute for" , "Substitute, supplant" , "Substitute for (someone)" , "Put something back where it belongs" , "Put back in original position" .)