spec·u·lum 
(spĕkyə-ləm)
(spĕkyə-ləm)n. pl. spec·u·la (-lə) or spec·u·lums
1. A mirror or polished metal plate used as a reflector in optical instruments.
2. An instrument for dilating the opening of a body cavity for medical examination.
3. Zoology
a. A bright, often iridescent patch of color on the wings of certain birds, especially ducks.
b. A transparent spot in the wings of some butterflies or moths.
[Middle English, surgical speculum, from Latin, mirror, from specere, to look at; see spek- in the Appendix of Indo-European roots.]