Group of three almost consuming four trifles (6)
I believe the answer is:
trivia
'trifles' is the definition.
(thesaurus)
'group of three almost consuming four' is the wordplay.
'group of three' becomes 'triad' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'consuming' is an insertion indicator.
'four' becomes 'iv' (roman numeral).
'triad' with its last letter taken off is 'tria'.
'tria' placed around 'iv' is 'TRIVIA'.
(Other definitions for trivia that I've seen before include "The details of little or no importance" , "Trifles, unimportant details" , "Useless facts" , "Small beer" , "relatively unimportant matters" .)