Brief sharp pain (6)
I believe the answer is:
twinge
'brief sharp pain' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for twinge that I've seen before include "Slight pang, maybe of conscience" , "Slight pain (of conscience?)" , "A small pang, of pain or concience" , "Sharp localised pain" , "Small, sharp pain" .)