Pervert isn't commonly getting slap (3,5)
I believe the answer is:
war paint
'slap' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'pervert isn't commonly getting' is the wordplay.
'pervert' becomes 'warp' (I've seen this in another clue).
'isn't commonly' becomes 'ain't' (non-standard version of 'isn't').
'getting' says to put letters next to each other.
'warp'+'aint'='WAR-PAINT'
Can you help me to learn more?
(Other definitions for war paint that I've seen before include "what woman may have to face" , "Facial decoration showing hostile intent" , "Make-up (for native Americans?)" , "put on a brave face?" , "Cosmetics" .)