\Spec"u*lum\, n.; pl. L. {Specula}, E. {Speculum}. [L.,
fr. specere to look, behold. See {Spy}.]
1. A mirror, or looking-glass; especially, a metal mirror, as
   in Greek and Roman arch[ae]ology.
2. A reflector of polished metal, especially one used in
   reflecting telescopes. See {Speculum metal}, below.
3. (Surg.) An instrument for dilating certain passages of the
   body, and throwing light within them, thus facilitating
   examination or surgical operations.
4. (Zo["o]l.) 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.
{Speculum metal}, a hard, brittle alloy used for making the
   reflectors of telescopes and other instruments, usually
   consisting of copper and tin in various proportions, one
   of the best being that in which there are 126.4 parts of
   copper to 58.9 parts of tin, with sometimes a small
   proportion of arsenic, antimony, or zinc added to improve
   the whiteness.