About duke being a dishonourable person (3)
I believe the answer is:
cad
'a dishonourable person' is the definition.
'about duke' is the wordplay.
'about' becomes 'ca' (abbreviation for 'circa'**).
'duke' becomes 'd'.
'ca'+'d'='CAD'
'being' is the link.
(Other definitions for cad that I've seen before include "Rotter, bounder" , "Stinker" , "designing software" , "A rotter, by Jove" , "A rotten chap, no integrity" .)