Happiest reunion out of school ends in commemoration (7)

I believe the answer is:

epitaph

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'commemoration' is the definition.
(epitaph is a kind of commemoration)

I can't explain the rest of the clue.

(Other definitions for epitaph that I've seen before include "Grave words" , "Words carved on a gravestone" , "Grave message" , "Words on the defunct" , "Tombstone inscription" .)

I've seen this clue in The Hindu.

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