Pant (4)
I believe the answer is:
gasp
'pant' is the definition.
(I know that pant can be written as gasp)
This is all the clue.
(Other definitions for gasp that I've seen before include "Short laboured intake of breath" , "Say "ah"" , "Fight for breath" , "Draw breath sharply" , "Noisily breathe" .)