Toothy smile (4)
I believe the answer is:
grin
'toothy smile' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for grin that I've seen before include "Accept with good grace - . . . . and bear it" , "Smile while pulling back the lips" , "Facial expression, usually of pleasure" , "Smile wryly" , "A broad smile showing the teeth" .)