1. Words or signs having no intelligible meaning: a message that was nonsense until decoded.
2. Subject matter, behavior, or language that is foolish or absurd.
3. Extravagant foolishness or frivolity: a clown's exuberant nonsense.
4. Matter of little or no importance or usefulness: a chatty letter full of gossip and nonsense.
5. Insolent talk or behavior; impudence: wouldn't take any nonsense from the children.