资料来源 : Webster's Revised Unabridged Dictionary (1913)

Rima \Ri"ma\, n.; pl. {Rim[ae]}. [L.] (Anat.)
   A narrow and elongated aperture; a cleft; a fissure.

资料来源 : WordNet®

rima
     n : a narrow elongated opening or fissure between two
         symmetrical parts
     [also: {rimae} (pl)]