Did he master his partner? (5)

I believe the answer is:

magog

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'did he' is the definition.
The definition suggests a singular noun which matches the answer.

'master his partner?' is the wordplay.
'master' becomes 'MA' (Master of Arts).
'his partner?' becomes 'gog' (I am not sure about this - if you are sure you should believe this answer much more).
'ma'+'gog'='MAGOG'

Can you help me to learn more?

(Other definitions for magog that I've seen before include "Gog and -, City of London guardian giants" , "Biblical king" , "Last of two old giants" , "Gog's companion" , "old giant" .)

I've seen this clue in the Evening Standard.

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