semilunar valve

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

• noun Either of two valves, one located at the opening of the aorta and the other at the opening of the pulmonary artery, each consisting of three crescent-shaped cusps and serving to prevent blood from flowing back into the ventricles.

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

• noun a heart valve with cusps shaped like half-moons; prevents blood from flowing back into the heart