Oscar and Carol after mischief in August (8)
I believe the answer is:
imposing
'august' is the definition.
(thesaurus)
'oscar and carol after mischief' is the wordplay.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'and' is a charade indicator (letters next to each other).
'carol' becomes 'sing' (carol can mean to sing carols).
'after' says to put letters next to each other.
'mischief' becomes 'imp' (mischievous creature).
'o' next to 'sing' is 'osing'.
'osing' put after 'imp' is 'IMPOSING'.
'in' acts as a link.
(Other definitions for imposing that I've seen before include "Taking liberties" , "Impressive - or putting tax on" , "Impressive in appearance" , "Grand, impressive" , "Enormous - levying - striking" .)