Limo

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early 20th century: from French, feminine adjective meaning ‘of Limousin’, originally denoting a caped cloak worn in Limousin (see Limousin1): originally the driver's seat of the car was outside in a separate compartment, covered with a canopy.

wiktionary

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Clipping of  limousine. 

etymonline

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limo (n.)

abbreviation of limousine, by 1959, American English.