Source : Webster's Revised Unabridged Dictionary (1913)

Nucellus \Nu*cel"lus\, n.; pl. {Nucelli}. [NL., dim. of nux,
   nucis, a nut.] (Bot.)
   See {Nucleus}, 3
   (a) .

Source : WordNet®

nucellus
     n : central part of a plant ovule; contains the embryo sac
     [also: {nucelli} (pl)]