Crossword Genius

Note unknown sauce (3)

Ross

I believe the answer is:

soy

'sauce' is the definition.
(soy sauce)

'note unknown' is the wordplay.
'note' becomes 'so' (musical note).
'unknown' becomes 'y' (algebra).
'so'+'y'='SOY'

(Other definitions for soy that I've seen before include "Piquant eastern sauce" , "Sauce bean" , "Dark salty sauce" , "Oriental sauce" , "Chinese sauce" .)

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