Dip in liquid (4)
I believe the answer is:
dunk
'dip in liquid' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dunk that I've seen before include "Dip (eg, biscuit) in drink" , "Dip into tea, say" , "Put into a liquid" , "Submerge in liquid" , "Immerse (a biscuit)" .)