Saw glutton tucking into English butter (7)
I believe the answer is:
epigram
'saw' is the definition.
(thesaurus)
'glutton tucking into english butter' is the wordplay.
'glutton' becomes 'pig' (I've seen this in another clue).
'tucking into' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'butter' becomes 'ram' (animal which butts).
'e'+'ram'='eram'
'pig' put within 'eram' is 'EPIGRAM'.
(Other definitions for epigram that I've seen before include "Clever remark" , "Witty poem" , "Form of wit" , "Bon mot" , "Short witty remark" .)