Happen to be unoriginal (5)

I believe the answer is:

recur

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'happen' is the definition.
(I know that recur is a more specific form of the action happen)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for recur that I've seen before include "come back to one's mind" , "Repeat" , "Be repeated" , "Return to mind" , "expected to return" .)

I've seen this clue in The Telegraph and The Globe and Mail.

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