Bright expression across mouth initially (4)
I believe the answer is:
beam
'bright expression across mouth initially' is the definition.
I can't judge whether this definition defines the answer.
'bright expression across mouth initially' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'bright expression across mouth' is 'BEAM'.
Can you help me to learn more?
(Other definitions for beam that I've seen before include "Ray - side" , "Ray of light or a large smile" , "Ray; structural timber" , "Apparatus used by women gymnasts" , "Smile radiantly" .)