Spit (6)
I believe the answer is:
saliva
'spit' is the definition.
(I know that spit can be written as saliva)
This is the entire clue.
(Other definitions for saliva that I've seen before include "Clear liquid secreted into the mouth" , "Oral secretion" , "body fluid" , "Liquid that moistens the mouth" , "Spit" .)