Smile . . . or shine (4)
I believe the answer is:
beam
I believe this is a double definition.
'smile' is the first definition.
(to beam is to smile)
'shine' is the second definition.
(I know that shine can be written as beam)
(Other definitions for beam that I've seen before include "Smile radiantly" , "Supporting piece of wood - shaft of light" , "Light - heavy timber - wide smile" , "Smile brightly - supporting timber" , "Smile broadly or radiate" .)