Smile (4)
I believe the answer is:
grin
'smile' is the definition.
(I know that grin is a more specific form of smile)
This is the entire clue.
(Other definitions for grin that I've seen before include "Wide smile" , "Accept with good grace - . . . . and bear it" , "Smile wryly" , "Ring (anag.)" , "A broad smile showing the teeth" .)