Singular, amusing insult (6)
I believe the answer is:
slight
'insult' is the definition.
(I've seen this before)
'singular amusing' is the wordplay.
'singular' becomes 's' (abbreviation in grammar).
'amusing' becomes 'light' (I've seen this before).
's'+'light'='SLIGHT'
(Other definitions for slight that I've seen before include "Small in degree; insult" , "Redeemer" , "A disrespectful reference - not great" , "Minor - insult" , "of no great significance" .)