Why is the ninth month called September?
c.1300, from Old French neveu (Old North French nevu) "grandson, descendant," from Latin nepotem (nominative nepos) "sister's son, grandson, descendant," in post-Augustan Latin, "nephew," from PIE *nepot- "grandchild," and in a general sense, "male descendant other than son" (cf. Sanskrit napat "grandson, descendant;" Old Persian napat- "grandson;" Old Lithuanian nepuotis "grandson;" Dutch neef; German Neffe "nephew;" Old Irish nia, genitive niath "son of a sister," Welsh nei). Used in English in all the classical senses until meaning narrowed in 17c., and also as a euphemism for "the illegitimate son of an ecclesiastic" (1580s). The Old English cognate, nefa "nephew, stepson, grandson, second cousin" survived to 16c.