A supportive smile? (4)
I believe the answer is:
beam
I believe this is a double definition.
'a supportive' is the first definition.
(I've seen this before)
'smile?' is the second definition.
(to beam is to smile)
(Other definitions for beam that I've seen before include "Piece of timber - shaft of light" , "Sturdy timber" , "Light - heavy timber - wide smile" , "Broadcast" , "Perhaps a summer" .)