1.NounA word considered obscene and vulgar or offensive.
"When I heard swear words from the next room, I decided to keep my distance.; Your kid said nasty swear words to me this morning."
2.NounA word that escapes someone's mind (and therefore often also their mouth) in a nearly automatic way when the person is under duress, mental stress or distress, etc; such words are often obscene and vulgar or offensive.