left wing

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The liberal or radical faction of a group.

from the GNU version of the Collaborative International Dictionary of English.

• noun Those trying to reform the established order, particularly in political matters, to enhance the condition of the common people; -- sometimes applied to those advocating overthrow of an existing government by radical means.

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

• noun politics the more left-wing faction of a group or party
• noun sports the left-hand side of a sports field
• noun ice hockey the offensive player who plays to the center's left

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

• noun those who support varying degrees of social or political or economic change designed to promote the public welfare