Michael is right that the verb is "to lunge," but the meaning is simply "to make a sudden forward movement." It can be a sudden movement of your arm (especially if you're holding a knife, sword, stick, etc.), but it often means moving forward with your whole body, not just your arm. As in Michael's example, it usually implies that you are going to attack something or someone.

The verb is to lunge. It means to reach forward with your arm. example: he lunged forward with a knife to attack the wild animal