Arr

wiktionary

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Abbreviation

Possibly from aye.

The pirate-imitation form was derived from the West Country dialect after its use by West Country-born actor Robert Newton (1905–1956) in the films Treasure Island (1950) and Blackbeard the Pirate (1952)—and the former’s spin-off media—in which he played, respectively, the fictional pirate Long John Silver and the historical pirate Edward “Blackbeard” Teach (c. 1680 – 1718; also a West Country native). [1] [2] [3]

etymonline

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arr (v.)

"to growl like a dog," late 15c., imitative. In classical times, the letter R was called littera canina "the dog letter" (Persius).