Lion's Tooth is the sword possessed by Prince Joffrey Baratheon. It's current location is unknown.
It was a longsword, made shorter so that it could be effectively used by a twelve year old boy. It is castle forged, made of gleaming blue steel, and is double edged. It has a leather grip, and a lion's head pommel.
Joffrey boasts of his sword when he takes Sansa Stark riding in The Riverlands. He compares it to the wooden swords that her brothers, Robb and Bran Stark, use when training. He uses the blade on Mycah when he is discovered sparring with Arya Stark, upon the girl's request. Arya attacks Joffrey, who is prevented from killing her by Nymeria, who attacks the prince. Arya then throws Joffrey's sword into the Trident, as a punishment for attacking her friend.