Hexadecimal

n. Base ₁₆. Coined in the early 1960s to replace earlier 'sexadecimal', which was too racy and amusing for stuffy IBM, and later adopted by the rest of the industry.

Actually, neither term is etymologically pure. If we take 'binary' to be paradigmatic, the most etymologically correct term for base 10, for example, is 'denary', which comes from 'deni' (ten at a time, ten each), a Latin 'distributive' number; the corresponding term for base-16 would be something like 'sendenary'. 'Decimal' is from an ordinal number; the corresponding prefix for 6 would imply something like 'sextidecimal'. The 'sexa-' prefix is Latin but incorrect in this context, and 'hexa-' is Greek. The word 'octal' is similarly incorrect; a correct form would be 'octaval' (to go with decimal), or 'octonary' (to go with binary). If anyone ever implements a base-3 computer, computer scientists will be faced with the unprecedented dilemma of a choice between two *correct* forms; both 'ternary' and 'trinary' have a claim to this throne.