n. Something to look into or from; specifically, a mirror or looking-glass.n. An attachment to or part of an optical instrument, as a reflecting telescope, having a brightly polished surface for the reflection of objects.n. In ornithology:n. An ocellus or eye-spot, as of a peacock's tail. See ocellus, 4.n. The mirror of a wing, a specially colored area on some of the flight-feathers.n. In anatomy, the septum lucidum of the brain. See cut under corpus.n. In medicine and surgery, an instrument used for rendering a part accessible to observation, especially by opening or enlarging an orifice.n. A lookout; a place to spy from.n. In astrology, a table exhibiting at one view the latitudes, destinations, semi-arcs, etc., of the planets in a nativity.