Fellow graduate catching minute butterfly (5)
I believe the answer is:
comma
'butterfly' is the definition.
(comma is a kind of butterfly)
'fellow graduate catching minute' is the wordplay.
'fellow' becomes 'co' (I've seen this in other clues**).
'graduate' becomes 'ma' (abbreviation for Master of Arts).
'catching' means one lot of letters goes inside another.
'minute' becomes 'm' (abbreviation).
'ma' enclosing 'm' is 'mma'.
'co'+'mma'='COMMA'
(Other definitions for comma that I've seen before include "I signal a break" , "Punctuation mark - butterfly" , "List-item separator" , "Clause-separating punctuation" , "its use may be divisive" .)