hexadecimal

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.