WordNet (r) 3.0 (2006):

hexadecimal
    adj 1: of or pertaining to a number system having 16 as its base
           [syn: hexadecimal, hex]

The Jargon File (version 4.4.7, 29 Dec 2003):

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.


The Free On-line Dictionary of Computing (30 December 2018):

hexadecimal
sexadecimal

    (Or "hex") Base 16.  A number representation
   using the digits 0-9, with their usual meaning, plus the
   letters A-F (or a-f) to represent hexadecimal digits with
   values of (decimal) 10 to 15.  The right-most digit counts
   ones, the next counts multiples of 16, then 16^2 = 256, etc.

   For example, hexadecimal BEAD is decimal 48813:

   	digit    weight        value
   	B = 11   16^3 = 4096   11*4096 = 45056
   	E = 14   16^2 =  256   14* 256 =  3584
   	A = 10   16^1 =   16   10*  16 =   160
   	D = 13   16^0 =    1   13*   1 =    13
   					 -----
   				BEAD   = 48813

   There are many conventions for distinguishing hexadecimal
   numbers from decimal or other bases in programs.  In C for
   example, the prefix "0x" is used, e.g. 0x694A11.

   Hexadecimal is more succinct than binary for representing
   bit-masks, machines addresses, and other low-level constants
   but it is still reasonably easy to split a hex number into
   different bit positions, e.g. the top 16 bits of a 32-bit word
   are the first four hex digits.

   The term was 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 ten, for example, is "denary", which comes from
   "deni" (ten at a time, ten each), a Latin "distributive"
   number; the corresponding term for base sixteen would be
   something like "sendenary".  "Decimal" is from an ordinal
   number; the corresponding prefix for six 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 three 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.

   [Jargon File]

   (1996-03-09)