collimation

Concise Oxford English Dictionary © 2008 Oxford University Press:
collimate /ˈkɒlɪmeɪt/

▶verb

• 1 make (rays of light or particles) accurately parallel.

• 2 accurately set the alignment of (an optical or other system).

– derivatives
collimation noun,
collimator noun.

– origin C19: from L. collimare, an erroneous reading of collineare ‘align or aim’.