ˌmēdēəˈstīnəm noun
( plural mediasti·na -nə)
Etymology: New Latin, from neuter of Latin mediastinus medial, from medius middle — more at mid
1. : the space in the chest between the pleural sacs of the lungs that contains all the viscera of the chest except the lungs and pleurae ; also : this space with its contents
2. : a mass of connective tissue at the back of the testis being continuous externally with the tunica albuginea and internally with the interlobular septa and enclosing the rete testis