x
     adj : being one more than nine [syn: {ten}, {10}]
     n 1: the cardinal number that is the sum of nine and one; the
          base of the decimal system [syn: {ten}, {10}, {tenner},
          {decade}]
     2: the 24th letter of the Roman alphabet
     3: street names for methylenedioxymethamphetamine [syn: {Adam},
         {ecstasy}, {XTC}, {go}, {disco biscuit}, {cristal}, {hug
        drug}]
Source: WordNet® 2.0

X /X/ n. 1. Used in various speech and writing contexts (also in
   lowercase) in roughly its algebraic sense of `unknown within a set
   defined by context' (compare {N}). Thus, the abbreviation 680x0 stands
   for 68000, 68010, 68020, 68030, or 68040, and 80x86 stands for 80186,
   80286, 80386, 80486, 80586 or 80686 (note that a Unix hacker might write
   these as 680[0-6]0 and 80[1-6]86 or 680?0 and 80?86 respectively; see
   {glob}). 2. [after the name of an earlier window system called `W'] An
   over-sized, over-featured, over-engineered and incredibly
   over-complicated window system developed at MIT and widely used on Unix
   systems.


Source: The Jargon File