Buckaroo

google

ref

early 19th century: alteration of vaquero.

wiktionary

ref

[1889], derived from Spanish vaquero(“cowboy”), from Vulgar Latin *vaccārius(“cowherder, rancher”); compare MerovingianLate Latin baccalarius(“cowherder serving under a farmer or feudal lord; a youth?”). Akin to vaca(“cow”), from Latin vacca +‎ -ero. Spelling influenced by buck. Cognate to French vacher, etc. Doublet of vaquero.

etymonline

ref

buckaroo (n.)

"cowboy," 1907, American English, earlier buckayro (1889), bakhara (1827), from Spanish vaquero "cowboy," from vaca "cow," from Latin vacca, a word of uncertain origin. Spelling altered by influence of buck (n.1).