Without his mum, he'd still have a partner (5)
I believe the answer is:
magog
'he'd still have a partner' is the definition.
The definition suggests a singular noun which matches the answer.
'without his mum' is the wordplay.
I cannot really see how this works, but
'mum' could be 'ma' (both can mean mother) and 'ma' is found within the answer.
The remaining letters 'gog' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for magog that I've seen before include "Biblical king" , "old giant" , "Last of two old giants" , "Gog's companion" , "Gog and -, City of London guardian giants" .)