The Collaborative International Dictionary of English v.0.48:

Graafian \Graaf"i*an\, a. (Anat.)
   Pertaining to, or discovered by, Regnier de Graaf, a Dutch
   physician.
   [1913 Webster]

   Graafian follicles or vesicles, small cavities in which the
      ova are developed in the ovaries of mammals, and by the
      bursting of which they are discharged.
      [1913 Webster]