The Collaborative International Dictionary of English v.0.48:

Mesoarium \Mes`o*a"ri*um\, n. [NL., from Gr. me`sos middle +
   'w,a`rion, dim. of 'w,o`n an egg.] (Anat.)
   The fold of peritoneum which suspends the ovary from the
   dorsal wall of the body cavity; the mesovarium.
   [1913 Webster]