Sapper out of breath, maybe! (7)
I believe the answer is:
perhaps
'maybe' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for perhaps that I've seen before include "Quite possibly" , "Possibly, maybe" , "Conceivably" , "say" , "Could be, maybe" .)