Source : Webster's Revised Unabridged Dictionary (1913)

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

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

   {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.

Source : WordNet®

achromatic
     adj 1: being of the achromatic color of maximum lightness; having
            little or no hue owing to reflection of almost all
            incident light; "as white as fresh snow"; "a bride's
            white dress" [syn: {white}] [ant: {black}]
     2: being of the achromatic color of maximum darkness; having
        little or no hue owing to absorption of almost all
        incident light; "black leather jackets"; "as black as
        coal"; "rich black soil" [syn: {black}] [ant: {white}]
     3: having no hue [ant: {chromatic}]