"the largest, most hideous, and most ferocious of the baboons" [OED], 1744, perhaps ultimately from a West African language, but formed into the English components man (n.) + drill (n.4) "baboon," which is of West African origin. The earliest reference reports the name is what the animal was "called by the white men in this country [Sierra Leone], but why it is so called I know not, nor did I ever hear of the Name before, neither can those who call them so tell, except it be for their near Resemblance of a human Creature, though nothing at all like an Ape." [William Smith, "A New Voyage to Guinea"]. French mandrill, Spanish mandril seem to be from English.