1) Disease of the aortum 
An aortic aneurysm is a general term for an enlargement (dilation) of the aorta to greater than 1.5 times normal size. While the cause of an aneurysm may be multifactorial, the end result is an underlying weakness in the wall of the aorta at that location. The aneurysm may occasionally cause pain, which is a sign of impending rupture. When rupture...
(from the article `aneurysm`) The symptoms of an aneurysm vary with the extent of the defect and its location. A person with an aortic aneurysm may not have symptoms until the ...
is a sac and/or dilation at some place in the aorta where the aorta artery wall may be weakened or damaged.
Dangeous ballooning of the aorta (the main artery leaving the heart) which is caused by disease in the artery's wall. ... (09 Oct 1997) ... 
aneurysm of the aorta.
Type: Term Definitions: 1. diffuse or circumscribed dilation of a portion of the aorta (abdominal aortic aneurysm, aortic arch aneurysm).
Aortic aneurysm: An outpouching (a local widening) of the largest artery in the body, the aorta, involving that vessel in its course above the diaphragm (thoracic aortic aneurysm) or, more commonly, below the diaphragm (abdominal aortic aneurysm). The diagnosis of an aortic aneurysm can be straight forward or difficult. Around 1900 the eminent phys...
[n] - an aneurysm of the aorta
noun an aneurysm of the aorta