The Collaborative International Dictionary of English v.0.48:

Collimate \Col"li*mate\, v. t. [imp. & p. p. Collimated; p. p.
   & vb. n. Collimating.] [See Collimation.] (Physics &
   Astron.)
   To render parallel to a certain line or direction; to bring
   into the same line, as the axes of telescopes, etc.; to
   render parallel, as rays of light.
   [1913 Webster]

   Collimating eyepiece, an eyepiece with a diagonal reflector
      for illumination, used to determine the error of
      collimation in a transit instrument by observing the image
      of a cross wire reflected from mercury, and comparing its
      position in the field with that of the same wire seen
      directly.

   Collimating lens (Optics), a lens used for producing
      parallel rays of light.
      [1913 Webster]

WordNet (r) 3.0 (2006):

collimate
    v 1: make or place parallel to something; "They paralleled the
         ditch to the highway" [syn: parallel, collimate]
    2: adjust the line of sight of (an optical instrument)