Why is the ninth month called September?
1570s, from Middle French acerbité, from Latin acerbitatem (nominative acerbitas) "harshness, sharpness, bitterness," from acerbus "bitter to taste, sharp, sour, tart" (related to acer "sharp;" cf. Latin superbus "haughty," from super "above"), from Proto-Italic *akro-po- "sharp," from PIE *ak- "sharp" (see acrid). Earliest use in English is figurative, of "sharp and bitter" persons. Of tastes, from 1610s.