Why is the ninth month called September?
late 14c., "to clothe in the official robes of an office," from Latin investire "to clothe in, cover, surround," from in "in, into" (see in- (2)) + vestire "to dress, clothe" (see wear). The meaning "use money to produce profit" first attested 1610s in connection with the East Indies trade, and is probably a borrowing of Italian investire (13c.) from the same Latin root, via the notion of giving one's capital a new form. The military meaning "to besiege" is from c.1600. Related: Invested; investing.