Refrain from commenting on stomach mark. (7)
I believe the answer is:
abstain
'refrain from' is the definition.
(abstaining is a kind of refraining from)
'commenting on stomach mark' is the wordplay.
I cannot really understand how this works, but
'mark' could be 'stain' (synonyms) and 'stain' is located in the answer.
The remaining letters 'ab' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for abstain that I've seen before include "Hold off" , "Avoid" , "Refrain from doing something" , "Go without" , "Withhold one's vote" .)