Aristos glower when interrupted by Spice Girl in retirement (8)
I believe the answer is:
noblemen
'aristos' is the definition.
(aristocrats)
'glower when interrupted by spice girl in retirement' is the wordplay.
'glower' becomes 'neon' (gas which glows).
'when interrupted by' is an insertion indicator (inserted letters interrupt).
'spice girl' becomes 'Mel B' (Mel B is a Spice Girls member).
'in retirement' shows that the letters should be reversed in order (retire can mean to go back or backwards).
'neon' enclosing 'melb' is 'nemelbon'.
'nemelbon' written backwards gives 'NOBLEMEN'.
(Other definitions for noblemen that I've seen before include "Aristocrats" , "Aristocrat, peer" , "Perhaps Lords" , "Peers" .)