Definitions of hexadecimal  [ˌhɛk səˈdɛs ə məl]  

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” comes from the combining root of decem, Latin for 10. If wish to create a truly analogous word for base 16, we should start with sedecim, Latin for 16. Ergo, sedecimal is the word that would have been created by a Latin scholar. 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.