Gnaw on cold chop (4)
I believe the answer is:
chew
'gnaw' is the definition.
(thesaurus)
'on cold chop' is the wordplay.
'on' means one lot of letters go next to another.
'cold' becomes 'c' (eg on taps).
'chop' becomes 'hew' (I've seen this in other clues**).
'c' put next to 'hew' is 'CHEW'.
(Other definitions for chew that I've seen before include "work with canines" , "What gossips do to fat" , "Prepare to swallow" , "Masticate, grind between teeth" , "champ" .)