Breathless piper is giving nothing away (7)
I believe the answer is:
deadpan
'giving nothing away' is the definition.
'breathless piper' is the wordplay.
'breathless' becomes 'dead' (similar in meaning).
'piper' becomes 'pan' (I've seen this in another clue).
'dead'+'pan'='DEADPAN'
'is' acts as a link.
(Other definitions for deadpan that I've seen before include "Betraying no emotion" , "with emotionless face" , "With expressionless face" , "Keeping a straight face" , "Dry" .)