Brilliant detailed revenue lesson (12)
I believe the answer is:
incomparable
'brilliant' is the definition.
(I know that brilliant can be written as incomparable)
'detailed revenue lesson' is the wordplay.
'detailed' means to remove the last letter (the word must be end-less or 'de-tailed').
'revenue' becomes 'income' (both can mean money made).
'lesson' becomes 'parable' (I've seen this before).
'income' with its final letter taken off is 'incom'.
'incom'+'parable'='INCOMPARABLE'
(Other definitions for incomparable that I've seen before include "Unrivalled" , "Matchless" , "Second-to-none" , "Unequalled" , "like no one else?" .)