Crossword Genius

Rum's not what the cure's made of (7)

Ross

I believe the answer is:

nostrum

I'm a little stuck... Click here to teach me more about this clue!

'of' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's an association between them I don't understand?

'rum's not what the cure's' is the wordplay.
'rum's not' anagrams to 'NOSTRUM'.
However, I am not sure how this is indicated.

'made' acts as a link.

Can you help me to learn more?

(Other definitions for nostrum that I've seen before include "Tonic" , "Some think it helps" , "Favourite remedy or scheme" , "secret potion" , "Hypothetical remedy for all ills" .)

I've seen this clue in The Globe and Mail.
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