With breathless humour! (3)
I believe the answer is:
wit
'humour' is the definition.
(I know that humour can be written as wit)
'with breathless' is the wordplay.
'with' becomes 'w' (short for with).
'breathless' becomes 'it' (I can't justify this - if you can you should give a lot more credence to this answer).
'w'+'it'='WIT'
Can you help me to learn more?
(Other definitions for wit that I've seen before include "Cleverness with words and ideas" , "Good sense" , "Quickness and cleverness with words" , "Ingenuity or verbal fun" , "Humour or mental capacity" .)