Why is the ninth month called September?
c.1300, from a Scandinavian source (cf. Old Norse myrr "bog, swamp"), from Proto-Germanic *miuzja- (cf. Old English mos "bog, marsh"), from PIE *meus- "damp" (see moss).
c.1400, in figurative sense of "to involve in difficulties," from mire (n.). Literal sense is from 1550s. Related: Mired; miring.
Any of the test objects on the arm of a keratometer whose image, as reflected on the curved surface of the cornea, is used in calculating the amount of astigmatism.