Webster's Dictionary 
(1): ( a.) First, precedent, or superior in the order of cognition, reason or generality, origin, development, rank, etc.
(2): ( a.) The superior of a priory, and next below an abbot in dignity.
(3): ( a.) Preceding in the order of time; former; antecedent; anterior; previous; as, a prior discovery; prior obligation; - used elliptically in cases like the following: he lived alone [in the time] prior to his marriage.
Charles Buck Theological Dictionary 
The head of a convent; next in dignity to an abbot.