Desire engineers showing brilliance (6)
I believe the answer is:
lustre
'brilliance' is the definition.
(I've seen this before)
'desire engineers' is the wordplay.
'desire' becomes 'lust' (lusting is a kind of desiring).
'engineers' becomes 're' (Royal Engineers).
'lust'+'re'='LUSTRE'
'showing' acts as a link.
(Other definitions for lustre that I've seen before include "Gentle sheen, soft glow" , "Distinction < in five years" , "Polish" , "Gloss, brightness" , "Brightness from reflected light" .)