mediastinum noun. [,mi:dɪǝ'stʌɪnǝm] Pl. -na [-nǝ]. Orig. also Anglicized as mediastine. LME.
[Neut. of medieval Latin mediastinus medial, from Latin = a low class of slave, from medius MID adjective.]
Anatomy. A partition between two body cavities or two parts of an organ; esp. that dividing the thorax, separating the right and left pleural cavities. Also, the space in the thorax between the pleural sacs, containing the heart, aorta, trachea, oesophagus, thymus, etc.

■ mediastinal adjective E19.

■ mediasti'nitis noun inflammation of the mediastinum of the thorax M19.

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