Main Entry: me·di·as·ti·num

Pronunciation: \ˌmēd-ē-ə-ˈstī-nəm\

Function: noun

Inflected Form(s): plural me·di·as·ti·na \-nə\

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 : mediastinum testis