The Collaborative International Dictionary of English v.0.48:

Aorta \A*or"ta\, n. [NL., fr. Gr. ?, fr. ? to lift, heave.]
   (Anat.)
   The great artery which carries the blood from the heart to
   all parts of the body except the lungs; the main trunk of the
   arterial system.
   [1913 Webster]

   Note: In fishes and the early stages of all higher
         vertebrates the aorta divides near its origin into
         several branches (the aortic arches) which pass in
         pairs round the [oe]sophagus and unite to form the
         systemic aorta. One or more pairs of these arches
         persist in amphibia and reptiles, but only one arch in
         birds and mammals, this being on the right side in the
         former, and on the left in the latter.
         [1913 Webster]
         [1913 Webster]

WordNet (r) 3.0 (2006):

aorta
    n 1: the large trunk artery that carries blood from the left
         ventricle of the heart to branch arteries