Earthquake (5)

I think it could be either:

Which length description are you looking for?:

seism

'earthquake' is the definition.
(I know that earthquake can be written as seism)

This is all the clue.

(Another definition for seism that I've seen is " Earth-shattering event".)

I've seen this clue in the Newsday, The Sunday Times and the King Feature Syndicate.

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