The Collaborative International Dictionary of English v.0.48:

Stroboscope \Strob"o*scope\, n. [Gr. ? a whirling + -scope.]
   1. An instrument for studying or observing the successive
      phases of a periodic or varying motion by means of light
      which is periodically interrupted.
      [1913 Webster]

   2. An optical toy similar to the phenakistoscope. See
      Phenakistoscope.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stroboscope
    n 1: scientific instrument that provides a flashing light
         synchronized with the periodic movement of an object; can
         make moving object appear stationary [syn: stroboscope,
         strobe, strobe light]