<p><strong>Noun:</strong></p><ul><li>the foremost division or the front part of an army; advance guard; van.</li><li>the forefront in any movement, field, activity, or the like.</li><li>the leaders of any intellectual or political movement.</li><li>(initial capital letter) Rocketry. a U.S. three-stage, satellite-launching rocket, the first two stages powered by liquid-propellant engines and the third by a solid-propellant engine.</li></ul>