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 &
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.
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
Collimating lens (Optics), a lens used for producing
parallel rays of light.