A new addition to the menage - a super piano (4,5)
I believe the answer is:
baby grand
'piano' is the definition.
(baby grand is a kind of piano)
'a new addition to the menage a super' is the wordplay.
I cannot really understand how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for baby grand that I've seen before include "Instrument" , "Smaller piano" , "message of proud new parents?" , "Small, non-upright piano" , "Infant piano?" .)