speculum

A mirror or polished metal plate used as a reflector in optical instruments.

An instrument for dilating the opening of a body cavity for medical examination.

A bright, often iridescent patch of color on the wings of certain birds, especially ducks.

A transparent spot in the wings of some butterflies or moths.

In astrology, a table exhibiting at one view the latitudes, destinations, semi-arcs, etc., of the planets in a nativity.

Something to look into or from; specifically, a mirror or looking-glass.

An attachment to or part of an optical instrument, as a reflecting telescope, having a brightly polished surface for the reflection of objects.

In ornithology:

An ocellus or eye-spot, as of a peacock’s tail. See ocellus, 4.