Not initially insulting illumination (8)
I believe the answer is:
lighting
'illumination' is the definition.
(I know that lighting is a type of illumination)
'not initially insulting' is the wordplay.
'not initially' means to remove the first letter.
'insulting' becomes 'slighting' (I've seen this before).
'slighting' with its first letter removed is 'LIGHTING'.
(Other definitions for lighting that I've seen before include "What bulbs can provide" , "Illuminating" , "Visual aids" , "See 14" , "landing" .)