The Collaborative International Dictionary of English v.0.48:

Stylus \Sty"lus\, n. [L. stylus, or better stilus.]
   1. An instrument for writing. See Style, n., 1.
      [1913 Webster]

   2. That needle-shaped part at the tip of the playing arm of
      phonograph which sits in the groove of a phonograph record
      while it is turning, to detect the undulations in the
      phonograph groove and convert them into vibrations which
      are transmitted to a system (since 1920 electronic) which
      converts the signal into sound; also called needle. The
      stylus is frequently composed of a hard metal or of
      diamond.
      [PJC]

   3. The needle-like device used to cut the grooves which
      record the sound on the original disc during recording of
      a phonograph record; it is moved by the vibrations given
      to the diaphragm by a sound, and produces the indented
      record.
      [PJC]

   4. (Computers) A pen-shaped pointing device used to specify
      the cursor position on a graphics tablet.
      [PJC] Stymie

WordNet (r) 3.0 (2006):

stylus
    n 1: a sharp pointed device attached to the cartridge of a
         record player
    2: a pointed tool for writing or drawing or engraving; "he drew
       the design on the stencil with a steel stylus" [syn:
       stylus, style]