The Collaborative International Dictionary of English v.0.48:

Confessor \Con*fess"or\ (?; 277), n. [OF. confessor, F.
   confesseur, fr. L. & LL. confessor.]
   1. One who confesses; one who acknowledges a fault, or the
      truth of a charge, at the risk of suffering; specifically,
      one who confesses himself a follower of Christ and endures
      persecution for his faith.
      [1913 Webster]

            He who dies for religion is a martyr; he who suffers
            for it is a confessor.                --Latham.
      [1913 Webster]

            Our religion which hath been sealed with the blood
            of so many martyrs and confessors.    --Bacon.
      [1913 Webster]

   2. A priest who hears the confessions of others and is
      authorized to grant them absolution.
      [1913 Webster]

WordNet (r) 3.0 (2006):

confessor
    n 1: a priest who hears confession and gives absolution
    2: someone who confesses (discloses information damaging to
       themselves)

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CONFESSOR, evid. A priest of some Christian sect, who receives an account of
the sins of his people, and undertakes to give them absolution of their
sins.
     2. The general rule on the subject of giving evidence of confidential
communications is, that the privilege is confined to counsel, solicitors,
and attorneys, and the interpreter between the counsel and the client. Vide
Confidential Communications. Contrary to this general rule, it has been
decided in New York, that a priest of the Roman Catholic denomination could
not be compelled to divulge secrets which he had received in auricular
confession. 2 City Hall Rec. 80, n.; Joy on Conf. Sec. 4, p. 49. See Bouv.
Inst. n. 3174 and note.