Crossword Genius

A number to play with supposedly curative powers (7)

Ross

I believe the answer is:

nostrum

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'with supposedly curative powers' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'a number to play' is the wordplay.
'a number' becomes 'no.' (abbreviation for 'number').
'to play' becomes 'strum' (I've seen this before).
'no'+'strum'='NOSTRUM'

Can you help me to learn more?

(Other definitions for nostrum that I've seen before include "Patent medicine of highly questionable value" , "Ineffective medicine" , "Tonic" , "Panacea or cure-all" , "Hypothetical remedy for all ills" .)

I've seen this clue in the Evening Standard.
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