Jiffy

google

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late 18th century: of unknown origin.

wiktionary

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Origin unknown; said to have been thieves’ cant for “lightning”. Also formerly written "giffy", to which a connection with gliff has been proposed. [1] As a kind of envelope, a genericization of Jiffy bag.

etymonline

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jiffy (n.)

1785, "a moment, an instant, short space of time," colloquial, origin unknown; said to have been thieves' slang for "lightning."