party whip

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun politics Within a legislative body, a member appointed by a political party and given the authority to ensure that all members of that party participate in voting and vote strictly as directed by the party in all votes where adherence to a party line is required.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a legislator appointed by the party to enforce discipline