Swallow hard
I believe the answer is:
gulp
'swallow hard' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gulp that I've seen before include "Noise made when swallowing too quickly" , "Swallow noisily" , "Swallow quickly" , "Swallow audibly" , "Audible swallow" .)