Stare in disbelief (4)
I believe the answer is:
gape
'stare in disbelief' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gape that I've seen before include "Failure to meet" , "watch in wonder" , "Stare at page" , "Peer" , "Look with mouth wide open" .)