AAA (abdominal aortic aneurysm): Many Americans know that the AAA ("triple A") is short for the American Automobile Association. Fewer may be aware that it is also the acronym for the American Association of Anatomists, one of a multitude of professional societies in the health arena. The AMA (the American Medical Association) is a far better known example. Only a small selection of these health-related organizations is given as a sampler in this DICTIONARY. The abbreviation AAA also stands for abdominal aortic aneurysm, a ballooning of the largest artery (the aorta) as it courses down through the abdomen. At the point of an abdominal aneurysm, the aneurysm usually measures 3 cm or more in diameter. The aneurysm weakens the wall of the aorta and can end in the aorta rupturing with catastrophic consequences. As the diameter of the aorta increases, the chances of an an abdominal aortic aneurysm rupturing rise commensurately. A measurement of 5 cm is often used to recommend surgery. Persons with abdominal aortic aneurysm tend to be 60 or over and are 5 times more likely to be male than female.