Radiate; grin (4)
I believe the answer is:
beam
I believe this is a double definition.
'radiate' is the first definition.
(synonyms)
'grin' is the second definition.
(I have seen 'Wide grin' mean 'beam' so perhaps 'grin' could also mean 'beam')
(Other definitions for beam that I've seen before include "Ray; structural timber" , "Smile radiantly" , "Ray; piece of timber" , "Column of light" , "Smile brightly - supporting timber" .)