The Collaborative International Dictionary of English v.0.48:

Choroid \Cho"roid\, a. [gr. ?; ? chorion + e'i^dos form.]
   (Anat.)
   resembling the chorion; as, the choroid plexuses of the
   ventricles of the brain, and the choroid coat of the eyeball.
   -- n. The choroid coat of the eye. See Eye.
   [1913 Webster]

   Choroid plexus (Anat.), one of the delicate fringelike
      processes, consisting almost entirely of blood vessels,
      which project into the ventricles of the brain.
      [1913 Webster]

WordNet (r) 3.0 (2006):

choroid plexus
    n 1: a vascular plexus of the cerebral ventricles that regulate
         intraventricular pressure [syn: choroid plexus, plexus
         choroideus]