Take up or perform in a suitable case (5)

I believe the answer is:

adopt

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'take up' is the definition.
(synonyms)

'perform in a suitable case' is the wordplay.
'perform' becomes 'do' (synonyms).
'in' is an insertion indicator.
'a suitable case' becomes 'apt' (I can't justify this - if you can you should give a lot more credence to this answer).
'do' going into 'apt' is 'ADOPT'.

'or' acts as a link.

Can you help me to learn more?

(Other definitions for adopt that I've seen before include "Take responsibility for" , "Embrace" , "Take into one's family" , "Choose as one's own" , "Assume (attitude)" .)

I've seen this clue in the Evening Standard.

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