Why is the ninth month called September?
c.1400, "unusual behavior," also "singleness of aim or purpose," from Old French singulerte "peculiarity" (12c., Modern French singularité) or directly from Late Latin singularitatem (nominative singularitas) "a being alone," from singularis (see singular (adj.)). Meaning "fact of being different from others" is c.1500. Mathematical sense of "point at which a function takes an infinite value" is from 1893. Astronomical use is from 1965.