A German mug? Definitely not! (8)

I believe the answer is:

einstein

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'definitely not' is the definition.
I can't tell whether this definition defines the answer.

'a german mug?' is the wordplay.
'a german' becomes 'ein' ('a' in German).
'mug?' becomes 'stein' (stein is a kind of mug).
'ein'+'stein'='EINSTEIN'

Can you help me to learn more?

(Other definitions for einstein that I've seen before include "Mathematical genius of nineties" , "Clever clogs finding" , "German physicist in the mad nineties" , "Albert -, famous scientist" , "Bavarian" .)

I've seen this clue in The Independent.

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