Perspiration (5)
I believe the answer is:
sweat
'perspiration' is the definition.
(I know that perspiration can be written as sweat)
This is all the clue.
(Other definitions for sweat that I've seen before include "Salty fluid secreted by glands" , "It's hard work" , "(Of argument) intense" , "Trouble in Australia" , "Soldier" .)