Stares slack-jawed (5)
I believe the answer is:
gapes
'stares slack-jawed' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gapes that I've seen before include "Yawns" , "goggles" , "Looks on with open mouth" , "Looks amazedly into pages" , "Stares at with mouth wide open" .)