The Collaborative International Dictionary of English v.0.48:

Mericarp \Mer"i*carp\, n. [Gr. me`ros a part + karpo`s fruit.]
   (Bot.)
   One carpel of an umbelliferous fruit. See Cremocarp.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mericarp
    n 1: a carpel with one seed; one of a pair split apart at
         maturity