|—n , pl -na|
|1.||a membrane between two parts of an organ or cavity such as the pleural tissue between the two lungs|
|2.||the part of the thoracic cavity that lies between the lungs, containing the heart, trachea, etc|
|[C16: from medical Latin, neuter of Medieval Latin mediastīnus median, from Latin: low grade of servant, from medius mean]|
mediastinum me·di·as·ti·num (mē'dē-ə-stī'nəm)
n. pl. me·di·as·ti·na (-nə)
A septum between two parts of an organ or a cavity.