The Collaborative International Dictionary
Thoracic \Tho*rac"ic\, a. [Cf. F. thoracique.] (Anat.) Of or pertaining to the thorax, or chest.
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.
WordNet
n. the major duct of the lymphatic system
Wikipedia
In human anatomy, the thoracic duct is the largest lymphatic vessel of the lymphatic system. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal. It carries chyle, a liquid containing both lymph and emulsified fats, rather than pure lymph. Thus when it ruptures, the resulting flood of liquid into the pleural cavity is known as chylothorax.
In adults, the thoracic duct is typically 38–45 cm in length and has an average diameter of about 5 mm. The vessel usually starts from the level of the twelfth thoracic vertebrae (T12) and extends to the root of the neck. It drains into the systemic (blood) circulation at the left subclavian vein. It also collects most of the lymph in the body other than from the right thorax, arm, head and neck which are drained by the right lymphatic duct.