Crossword Genius

A number quietly on edge (3)

Ross

I believe the answer is:

lip

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'on edge' is the definition.
(I've seen this before)

'a number quietly' is the wordplay.
'a number' becomes 'li' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'quietly' becomes 'p' (p for piano and quiet).
'li'+'p'='LIP'

Can you help me to learn more?

(Other definitions for lip that I've seen before include "sauciness" , "Rim; impudence (slang)" , "Edge; impudence" , "giving such insincere service" , "Top edge of a vessel" .)

I've seen this clue in the Evening Standard.
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