If motherless, he'd still have a partner (5)
I believe the answer is:
magog
'if motherless he'd still have a partner' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for magog that I've seen before include "Last of two old giants" , "Biblical king" , "old giant" , "Gog and -, City of London guardian giants" , "Gog's companion" .)