Source : Webster's Revised Unabridged Dictionary (1913)

Prioress \Pri"or*ess\, n. [OF. prioresse.]
   A lady superior of a priory of nuns, and next in dignity to
   an abbess.

Source : WordNet®

prioress
     n : the superior of a group of nuns [syn: {abbess}, {mother
         superior}]