Set off, forgetting meeting in school (4)

I believe the answer is:

eton

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'school' is the definition.
(famous UK public school)

I don't understand the remainder of the clue.

(Other definitions for eton that I've seen before include "Posh college" , "Famous college" , "Town opposite Windsor on the Thames" , "School near Slough" , "School; jacket type" .)

I've seen this clue in The Telegraph.

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