speculum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A mirror or polished metal plate used as a reflector in optical instruments.
2. n. An instrument for dilating the opening of a body cavity for medical examination.
3. n. Zoology A bright, often iridescent patch of color on the wings of certain birds, especially ducks.
4. n. Zoology A transparent spot in the wings of some butterflies or moths.

Century Dictionary and Cyclopedia

1. n. Something to look into or from; specifically, a mirror or looking-glass.
2. n. An attachment to or part of an optical instrument, as a reflecting telescope, having a brightly polished surface for the reflection of objects. Specula are generally made of an alloy called speculum-metal, consisting of ten parts of copper to one of tin, sometimes with a little arsenic to increase its whiteness. Another speculum alloy is made of equal weights of steel and platinum. Specula are also made of glass covered with a film of silver on the side turned toward the objects.
3. n. In ornithology:
4. n. An ocellus or eye-spot, as of a peacock's tail. See ocellus, 4.
5. n. The mirror of a wing, a specially colored area on some of the flight-feathers. It is usually iridescent-green, purple, violet, etc., and formed by a space of such color on the outer webs of several secondaries, toward their end, and commonly set in a frame of different colors formed by the tips of the same secondaries or of the greater wing-coverts, or of both. Sometimes it is dead-white, as in the gadwall. A speculum occurs in various birds, and as a rule in ducks, especially the Anatinæ, being in these so constant and characteristic a marking that some breeds of game-fowls are named duckwing in consequence of a certain resemblance in the wing-markings. See silver-duckwing. Also called mirror. See cuts under Chaulelasmus and mallard.
6. n. In anatomy, the septum lucidum of the brain. See cut under corpus.
7. n. In medicine and surgery, an instrument used for rendering a part accessible to observation, especially by opening or enlarging an orifice.
8. n. A lookout; a place to spy from.
9. n. In astrology, a table exhibiting at one view the latitudes, destinations, semi-arcs, etc., of the planets in a nativity.

Wiktionary

1. n. medicine A medical instrument used during an examination to dilate an orifice.
2. n. A mirror.

GNU Webster's 1913

1. n. A mirror, or looking-glass; especially, a metal mirror, as in Greek and Roman archæology.
2. n. A reflector of polished metal, especially one used in reflecting telescopes. See Speculum metal, below.
3. n. (Surg.) An instrument for dilating certain passages of the body, and throwing light within them, thus facilitating examination or surgical operations.
4. n. (Zoöl.) A bright and lustrous patch of color found on the wings of ducks and some other birds. It is usually situated on the distal portions of the secondary quills, and is much more brilliant in the adult male than in the female.

WordNet 3.0

1. n. a mirror (especially one made of polished metal) for use in an optical instrument
2. n. a medical instrument for dilating a bodily passage or cavity in order to examine the interior