ˈ ̷ ̷ ̷ ̷ˌmād.ə(r) noun
( -s )
1. : a device for producing a beam of parallel rays of light or other radiation or for forming an infinitely distant virtual image that can be viewed without parallax usually consisting of a tube having an objective lens at the end toward the observer and a slit or cross hairs in the objective focal plane at the other end — see spectrometer illustration
2. : a device for obtaining a beam of molecules, atoms, or nuclear particles of limited cross section and moving in parallel lines