Door opener (4)

I think it could be either:

Which length description are you looking for?:

key

'door opener' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for key that I've seen before include "Coral reef off southern coast of Florida" , "Clue" , "Crucial; island" , "Lock-opener" , "Crucial arch-stone" .)

I've seen this clue in The Mirror and The New York Times.

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