Great setter's about to eat eg almond trifle (7)
I believe the answer is:
minutia
'trifle' is the definition.
(both can mean precise or unimportant details)
'great setter's about to eat eg almond' is the wordplay.
'great' becomes 'AI' (resembles Ai, old-fashioned term meaning very good).
'setter's' becomes 'im' (I am - referring to the crossword setter).
'about' is a reversal indicator.
'to eat' is an insertion indicator.
'eg almond' becomes 'nut' (almond is a type of nut).
'ai'+'im'='aiim'
'aiim' reversed gives 'miia'.
'miia' enclosing 'nut' is 'MINUTIA'.
(Other definitions for minutia that I've seen before include "Precise detail; small, trivial matter" , "A small or minor detail" , "Tiny detail" .)