optic

Short definition from Wiktionary

Adjective

1. 1
   Of, or relating to the eye or to vision.
2. 2
   Of, or relating to optics or optical instruments.

Noun

1. 1
   An eye.
2. 2
   A lens or other part of an optical instrument that interacts with light.
3. 3
   A measuring device with a small window, attached to an upside-down bottle, used to dispense alcoholic drinks in a bar.