Source : Webster's Revised Unabridged Dictionary (1913)

Tentorium \Ten*to"ri*um\, n. [L., a tent.] (Anat.)
   A fold of the dura mater which separates the cerebellum from
   the cerebrum and often incloses a process or plate of the
   skull called the bony tentorium.

Source : WordNet®

tentorium
     n : (anatomy) a fold of dura mater that covers the cerebellum
         and supports the occipital lobes of the cerebrum