Give the game away (4)
I believe the answer is:
blab
'give the game away' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for blab that I've seen before include "Talk indiscreetly" , "24 ac secrets in talk" , "Give the game away" , "Shoot one's mouth off" , "Let the cat out of the bag" .)