Gape (4)
I believe the answer is:
yawn
'gape' is the definition.
(I know that gape can be written as yawn)
This is all the clue.
(Other definitions for yawn that I've seen before include "Show tiredness/boredom" , "Show boredom" , "Bored sign" , "Show one is tired or bored" , "Open mouth wide" .)