Our cousin's a singer and a half (6)
I believe the answer is:
bonobo
'our cousin's' is the definition.
(close relative of humanity)
'a singer and a half' is the wordplay.
'a singer' becomes 'Bono' (singer from Uo).
'and' is a charade indicator (letters next to each other).
'a half' becomes 'bo' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'bono'+'bo'='BONOBO'
(Other definitions for bonobo that I've seen before include "Small chimpanzee" , "our nearest relative" .)