Wide smile gives support (4)
I believe the answer is:
beam
I believe this is a double definition.
'wide smile' is the first definition.
(I've seen this before)
'support' is the second definition.
(beam is a kind of support)
'gives' acts as a link.
(Other definitions for beam that I've seen before include "Smile; piece of timber" , "Perhaps a summer" , "Piece of timber - shaft of light" , "Smile broadly or radiate" , "Give a wide smile" .)