Why is the ninth month called September?
c.1600, "fact of being hated," from Latin odium "ill-will, hatred, grudge, animosity; offense, offensive conduct," related to odi "I hate" (infinitive odisse), from PIE root *od- "to hate" (cf. Armenian ateam "I hate," Old Norse atall, Old English atol "dire, horrid, loathsome"). Meaning "hatred, detestation" is from 1650s. Often in an extended form, e.g. odium theologicum "hatred which is proverbially characteristic of theological disputes" (1670s).