The Collaborative International Dictionary of English v.0.48:

Claustral \Claus"tral\, a. [F., fr. LL. claustralis, fr. L.
   claustrum. See Cloister.]
   Cloistral. --Ayliffe
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Claustrum \Claus"trum\, n.; pl. Claustra. [L., a bolt or bar.]
   (Anat.)
   A thin lamina of gray matter in each cerebral hemisphere of
   the brain of man. -- Claus"tral, a.
   [1913 Webster]