speculum

noun (plural specula /-lə/)

• 1 Medicine a metal instrument that is used to dilate an orifice or canal in the body to allow inspection.

• 2 Ornithology a bright patch of plumage on the wings of certain birds, especially a strip of metallic sheen on the secondary flight feathers of many ducks.

• 3a mirror or reflector of glass or metal, especially (formerly) a metallic mirror in a reflecting telescope.
• short for speculum metal.