Why is the ninth month called September?
Old English siftan "pass (something) through a sieve," from Proto-Germanic *sib- (cf. Dutch ziften, Middle Low German sichten, German sichten "to sift;" see sieve (n.)). Intransitive sense "to pass loosely or fall scatteredly" is from 1590s. Metaphoric sense of "look carefully through" first recorded 1530s. Related: Sifted; sifting.