**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.