(archaic, humorous) An eye.

(optics) A lens or other part of an optical instrument that interacts with light.

(trademark in UK) A measuring device with a small window, attached to an upside-down bottle, used to dispense alcoholic drinks in a bar.

(relational) Of, or relating to the eye or to vision.

(optics, relational) Of, or relating to optics or optical instruments.