hexadecimal

n. Base 16. Coined in the early 1950s 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 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.

