The Collaborative International Dictionary of English v.0.48:

Thoracic \Tho*rac"ic\, a. [Cf. F. thoracique.] (Anat.)
   Of or pertaining to the thorax, or chest.
   [1913 Webster]

   Thoracic duct (Anat.), the great trunk of the lymphatic
      vessels, situated on the ventral side of the vertebral
      column in the thorax and abdomen. See Illust. of
      Lacteal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

thoracic duct
    n 1: the major duct of the lymphatic system