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.