[1] : The Collaborative International Dictionary of English v.0.48

zona \zo"na\, n.; pl. zonae. l., a girdle. see zone.
   a zone or band; a layer.
   1913 webster

   zona pellucida. nl. biol.
   a the outer transparent layer, or envelope, of the ovum. it
       is a more or less elastic membrane with radiating striae,
       and corresponds to the cell wall of an ordinary cell. see
       ovum, and illust. of microscope.
   b the zona radiata.

   zona radiata nl. biol., a radiately striated membrane
      situated next the yolk of an ovum, or separated from it by
      a very delicate membrane only.
      1913 webster
see also:
zonae zone zona pellucida ovum microscope zona radiata 

[2] : WordNet (r) 2.0

zona
     n : anatomy any encircling or beltlike structure syn: zone
see also:
zone 

Zona >> Z Words
Zona, definition of term: Zona
zona_pag1.html

Zona Pellucida >> Z Words
Zona Pellucida, definition of term: Zona Pellucida
zona+pellucida_pag1.html