Contrariwise, is much more clean (8)
I believe the answer is:
spotless
'clean' is the definition.
(similar in meaning)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for spotless that I've seen before include "totally innocent" , "Absolutely pure, clean" , "showing no sign of acne?" , "Perfect" , "honest!" .)