Power line? (7)

I think it could be either:

Which length description are you looking for?:

dynasty

'power line?' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for dynasty that I've seen before include "House" , "Song, say" , "Power line" , "Line of kings" , "Series of hereditary rulers" .)

I've seen this clue in The Globe and Mail and the New York Times.

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