Pound calamari, removing head (4)
I believe the answer is:
quid
'pound' is the definition.
(UK slang for a pound)
'calamari removing head' is the wordplay.
'calamari' becomes 'squid' (synonyms).
'removing head' means to remove the first letter.
'squid' with its initial letter taken off is 'QUID'.
(Other definitions for quid that I've seen before include "Pound - lump of chewing tobacco" , "One pound sterling" , "Pound (sl.)" , "Wad of chewing tobacco" , "100p (slang)" .)