Slap raised lump on skin without discomfort (8)
I believe the answer is:
warpaint
'slap' is the definition.
(I've seen this before)
'raised lump on skin without discomfort' is the wordplay.
'raised lump on skin' becomes 'wart' (a wart is a lump on skin).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'discomfort' becomes 'pain' (I've seen this in another clue).
'wart' placed around 'pain' is 'WARPAINT'.
(Other definitions for warpaint that I've seen before include "Given slap" , "what belligerent Indian wore" , "Make-up (for native Americans?)" .)