collimator

noun

col·​li·​ma·​tor ˈkä-lə-ˌmā-tər 

1

: a device for producing a beam of parallel rays (as of light) or for forming an infinitely distant virtual image that can be viewed without parallax

2

: a device for obtaining a beam (as of particles) of limited cross section

Word History

First Known Use

1865, in the meaning defined at sense 1

Medical Definition

collimator

noun

col·​li·​ma·​tor ˈkäl-ə-ˌmāt-ər 

: a device for obtaining a beam of radiation (as X-rays) of limited cross section