Saying sliced pie good with butter (7)
I believe the answer is:
epigram
'saying' is the definition.
(I know that epigram is a type of saying)
'sliced pie good with butter' is the wordplay.
'sliced' indicates an anagram.
'good' becomes 'g' (abbreviation).
'with' is a charade indicator (letters next to each other).
'butter' becomes 'ram' (I've seen this before).
'pie' anagrammed gives 'epi'.
'epi'+'g'+'ram'='EPIGRAM'
(Other definitions for epigram that I've seen before include "Witty or sarcastic saying" , "Quip, witty saying" , "Clever remark" , "Witty poem" , "A short witty saying" .)