noun
: any of the crescentic cusps that occur as a set of three between the heart and the aorta and another of three between the heart and the pulmonary artery, are forced apart by pressure in the ventricles during systole and pushed together by pressure in the arteries during diastole, and prevent regurgitation of blood into the ventricles ; also : either set of three cusps : an aortic or pulmonary valve