The Collaborative International Dictionary of English v.0.48:

Stylet \Sty"let\, n. [F., dim. of style; cf. It. stiletto. See
   Stiletto.]
   A small poniard; a stiletto.
   [1913 Webster]

   2. (Surg.)
      (a) An instrument for examining wounds and fistulas, and
          for passing setons, and the like; a probe, -- called
          also specillum.
      (b) A stiff wire, inserted in catheters or other tubular
          instruments to maintain their shape and prevent
          clogging.
          [1913 Webster]

   3. (Zool.) Any small, more or less rigid, bristlelike organ;
      as, the caudal stylets of certain insects; the ventral
      stylets of certain Infusoria.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stylet
    n 1: small needlelike appendage; especially the feeding organ of
         a tardigrade