Everything in note demanding silence is somewhat implausible (7)

I believe the answer is:

tallish

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'somewhat implausible' is the definition.
I can't tell whether this defines the answer.

'everything in note demanding silence' is the wordplay.
'everything' becomes 'all' (all things).
'in' is an insertion indicator.
'note' becomes 'ti' (musical note, as in do re mi so fa la ti do).
'demanding silence' becomes 'sh' ('sh' is said to tell someone to be silent. I am not sure about the 'demanding' bit.).
'all' put into 'ti' is 'talli'.
'talli'+'sh'='TALLISH'

'is' acts as a link.

Can you help me to learn more?

(Other definitions for tallish that I've seen before include "Consider" , "Rather lofty" , "rather large" .)

I've seen this clue in The Guardian.

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