Check on boy reversed -- outrage (7)
I believe the answer is:
scandal
'outrage' is the definition.
(synonyms)
'check on boy reversed' is the wordplay.
'check' becomes 'scan' (I've seen this in another clue).
'on' says to put letters next to each other.
'boy' becomes 'lad' (informal term for boy).
'reversed' is a reversal indicator.
'lad' in reverse letter order is 'dal'.
'scan'+'dal'='SCANDAL'
(Other definitions for scandal that I've seen before include "outrageous behaviour" , "Public disgrace" , "Shocking disgrace" , "Outraging event" , "Shocking thing" .)