Voice disapproval about wealthy man, a relative of ours (6)
I believe the answer is:
bonobo
'a relative of ours' is the definition.
(bonobos are related to humans)
'voice disapproval about wealthy man' is the wordplay.
'voice disapproval' becomes 'boo' (to boo is to express disapproval).
'about' means one lot of letters goes inside another.
'wealthy man' becomes 'nob' (nob is a kind of wealthy man).
'boo' going around 'nob' is 'BONOBO'.
(Other definitions for bonobo that I've seen before include "our nearest relative" , "Small chimpanzee" .)