The Collaborative International Dictionary of English v.0.48:

Prior \Pri"or\, n. [OE. priour, OF. priour, prior, priur, F.
   prieur, from L. prior former, superior. See Prior, a.]
   1. (Eccl.) The superior of a priory, and next below an abbot
      in dignity.
      [1913 Webster]

   2. a chief magistrate, as in the republic of Florence in the
      middle ages. --[RHUD]
      [PJC]

   Conventical prior, or Conventual prior, a prior who is at
      the head of his own house. See the Note under Priory.

   Claustral prior, an official next in rank to the abbot in a
      monastery; prior of the cloisters.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Prior \Pri"or\, n.
   a prior conviction; -- said of an accused criminal.
   [informal]
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Prior \Pri"or\, a. [L. prior former, previous, better, superior;
   compar. corresponding to primus first, and pro for. See
   Former, and cf. Prime, a., and Pre-, Pro-.]
   1. 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.
      [1913 Webster]

   2. First, precedent, or superior in the order of cognition,
      reason or generality, origin, development, rank, etc.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

prior
    adj 1: earlier in time [syn: anterior, prior(a)]
    n 1: the head of a religious order; in an abbey the prior is
         next below the abbot

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "prior":
   ahead, ancient, antecedent, anterior, anticipatory, before, chief,
   ci-devant, earlier, early, elder, erstwhile, ex, exordial, first,
   fore, foregoing, foremost, former, forward, heading, headmost,
   immemorial, inaugural, initiatory, last, late, latest, leading,
   old, olden, older, once, onetime, past, precedent, preceding,
   precessional, precurrent, precursory, preexistent, prefatory,
   prehistoric, preliminary, preludial, prelusive, preparatory,
   prevenient, previous, previous to, prime, primeval, primitive,
   prior to, proemial, propaedeutic, quondam, recent, senior,
   sometime, then, till, until, whilom