Ray, come off it! (5)
I believe the answer is:
light
'ray' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for light that I've seen before include "Falling short of contract" , "Easily lifted" , "guide in the dark" , "What smoker may be requesting" , "Source of illumination" .)