Kimura (Brazilian Jiu-Jitsu), chicken wing/double wristlock (wrestling), or reverse keylock are terms used to specify a medial keylock known in judo as gyaku ude-garami (reverse arm entanglement) or simply as ude-garami.
The application is similar to the americana, except that it is reversed. It needs some space behind the opponent to be effective, and can be applied from the side control or guard. Contrary to the americana, the opponent's wrist is grabbed with the hand on the same side, and the opposite arm is put behind the opponent's arm, again grabbing the attacker's wrist and forming a figure-four. By controlling the opponent's body and cranking the arm away from the attacker, pressure is put on the shoulder joint, and depending on the angle, also the elbow joint (in some variations the opponent's arm is brought behind their back, resulting in a finishing position resembling that of the hammerlock).
The kimura was named after the judoka Kimura Masahiko, who used it to defeat one of the founders of Brazilian Jiu-Jitsu, Hélio Gracie. It is then popularized in pro wrestling by WWE wrestler Brock Lesnar, where he would use it often to break his opponent's arm, in storyline.