Disqualify the German always holding substance (10)

I believe the answer is:

deregister

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'disqualify' is the definition.
Both the answer and definition are verbs in their base form.
Perhaps they are linked in a way I don't understand?

'the german always holding substance' is the wordplay.
'the german' becomes 'der' ('the' in German).
'always' becomes 'eer' (poetic way of saying ever).
'holding' means one lot of letters goes inside another.
'substance' becomes 'gist' (synonyms).
'eer' enclosing 'gist' is 'egister'.
'der'+'egister'='DEREGISTER'

Can you help me to learn more?

(Another definition for deregister that I've seen is " With strike off".)

I've seen this clue in the Sydney Morning Herald.

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