It's a long story (4)

I think it could be either:

yarn

saga

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'long story' is the definition.

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

(Other definitions for yarn that I've seen before include "Story, and thread or wool, say" , "Long involved story" , "Rope" , "Rambling story" , "Spun thread; long story" .)

I've seen this clue in The New York Times, the Newsday, the Evening Standard, the Universal, The Washington Post, the USA Today, The Guardian and The Wall Street Journal.

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