Definition of "speculum"

(medicine) A medical instrument used during an examination to dilate an orifice.  examples

A mirror, especially one used in a telescope.  examples

(ornithology) A bright, lustrous patch of colour found on the wings of ducks and some other birds, usually situated on the distal portions of the secondary quills, and much more brilliant in the adult male than in the female.

A lookout place.  examples