Origin of glow, a small lamp (8)
I believe the answer is:
gaslight
'lamp' is the definition.
(thesaurus)
'origin of glow a small' is the wordplay.
'origin of' indicates taking the first letters.
'small' becomes 'slight' (I've seen this before).
The initial letter of 'glow' is 'g'.
'g'+'a'+'slight'='GASLIGHT'
(Other definitions for gaslight that I've seen before include "that was illuminating for Fanny" , "Sort of illumination" , "Old film" , "Old-fashioned illumination" , "Bergman film" .)