Ring round for smile (4)
I believe the answer is:
grin
'smile' is the definition.
(grinning is a kind of smiling)
'ring round' is the wordplay.
'round' indicates an anagram.
'ring' with letters rearranged gives 'GRIN'.
'for' acts as a link.
(Other definitions for grin that I've seen before include "Look pleased" , "A broad smile showing the teeth" , "Happy expression" , "Give a broad smile" , "Smile broadly showing teeth" .)