swear [OE] This first meant ‘to make a solemn declaration’. The use of swear in connection with bad language came towards the end of the 14th century, as an extension of the idea of using a sacred name in an oath. Someone who swears a lot can be said to swear like a trooper [M18th]. A trooper was originally a private soldier in a cavalry unit. By the 18th century these soldiers had developed a reputation for coarse behaviour and bad language. Answer [OE] comes from the same root, and originally meant to rebut an accusation, literally ‘swear against’.