Heartless imp tucking into spread served up for gnome (7)
I believe the answer is:
epigram
'gnome' is the definition.
(thesaurus)
'heartless imp tucking into spread served up' is the wordplay.
'heartless' suggests removing the centre.
'tucking into' indicates putting letters inside.
'spread' becomes 'marge' (marge is a kind of spread**).
'served up' is a reversal indicator.
'imp' with its centre removed is 'ip'.
'ip' going into 'marge' is 'margipe'.
'margipe' backwards is 'EPIGRAM'.
'for' acts as a link.
(Other definitions for epigram that I've seen before include "Clever remark" , "Pithy and witty saying" , "Snappy piece of wit" , "witty comment" , "Witticism - adage" .)