speclum -
n. (pl. specula)
1 Surgery an instrument for dilating the cavities of the human
body for inspection.
2 a mirror, usu. of polished metal, esp. in a reflecting telescope.
3 Ornithol. a lustrous coloured area on the wing of some birds, esp. ducks.
speculum-metal an alloy of copper and tin used as a mirror, esp. in a telescope. [L, = mirror, f. specere look]