The Collaborative International Dictionary of English v.0.48:

Nucleole \Nu"cle*ole\, n. [See Nucleolus.]
   The nucleus within a nucleus; nucleolus.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nucleole
    n 1: a small round body of protein in a cell nucleus; such
         organelles contain RNA and are involved in protein
         synthesis [syn: nucleolus, nucleole]