The Collaborative International Dictionary of English v.0.48:

Achromatic \Ach`ro*mat"ic\, a. [Gr. 'achrw`matos colorless; 'a
   priv. + chrw^ma, chrw`matos, color: cf. F. achromatique.]
   1. (Opt.) Free from color; transmitting light without
      decomposing it into its primary colors.
      [1913 Webster]

   2. (Biol.) Uncolored; not absorbing color from a fluid; --
      said of tissue.
      [1913 Webster]

   Achromatic lens (Opt.), a lens composed usually of two
      separate lenses, a convex and concave, of substances
      having different refractive and dispersive powers, as
      crown and flint glass, with the curvatures so adjusted
      that the chromatic aberration produced by the one is
      corrected by other, and light emerges from the compound
      lens undecomposed.

   Achromatic prism. See Prism.

   Achromatic telescope, or microscope, one in which the
      chromatic aberration is corrected, usually by means of a
      compound or achromatic object glass, and which gives
      images free from extraneous color.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Microscope \Mi"cro*scope\, n. [Micro- + -scope.]
   An optical instrument, consisting of a lens, or combination
   of lenses, for making an enlarged image of an object which is
   too minute to be viewed by the naked eye.
   [1913 Webster]

   Compound microscope, an instrument consisting of a
      combination of lenses such that the image formed by the
      lens or set of lenses nearest the object (called the
      objective) is magnified by another lens called the ocular
      or eyepiece.

   Oxyhydrogen microscope, and Solar microscope. See under
      Oxyhydrogen, and Solar.

   Simple microscope, or Single microscope, a single convex
      lens used to magnify objects placed in its focus.
      [1913 Webster]

WordNet (r) 3.0 (2006):

microscope
    n 1: magnifier of the image of small objects; "the invention of
         the microscope led to the discovery of the cell"