Boy (n.)
Mid-13c., boie "servant, commoner, knave, boy," of unknown origin. Possibly from Old French embuie "one fettered," from Vulgar Latin *imboiare, from Latin boia "leg iron, yoke, leather collar," from Greek boeiai dorai "ox hides." (Words for "boy" double as "servant, attendant" across the Indo-European map – compare Italian ragazzo, French garçon, Greek pais, Middle English knave, Old Church Slavonic otroku – and often it is difficult to say which meaning came first.)

Source : Online Etymology Dictionary

Note: The Online Etymology Dictionary maintains a free-access list of the origins of thousands of English words, a significant proportion of which are unknown