TV off? Time for a short letter (7)

I believe the answer is:

notelet

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'short letter' is the definition.
(I have seen 'Short letter' mean 'notelet' so perhaps 'letter' could also mean 'notelet'; 'short' asks for an abbreviation)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for notelet that I've seen before include "Paper for informal letter" , "Small written communication" , "Small sheet for letter" , "Brief communication" , "Short folded letter" .)

I've seen this clue in The Guardian.

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