The Collaborative International Dictionary of English v.0.48:

Rector \Rec"tor\ (r?k"t?r), n. [L., fr. regere, rectum, to lead
   straight, to rule: cf. F. recteur. See Regiment, Right.]
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   1. A ruler or governor. [R.]
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            God is the supreme rector of the world. --Sir M.
                                                  Hale.
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   2.
      (a) (Ch. of Eng.) A clergyman who has the charge and cure
          of a parish, and has the tithes, etc.; the clergyman
          of a parish where the tithes are not impropriate. See
          the Note under Vicar. --Blackstone.
      (b) (Prot. Epis. Ch.) A clergyman in charge of a parish.
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   3. The head master of a public school. [Scot.]
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   4. The chief elective officer of some universities, as in
      France and Scotland; sometimes, the head of a college; as,
      the Rector of Exeter College, or of Lincoln College, at
      Oxford.
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   5. (R. C. Ch.) The superior officer or chief of a convent or
      religious house; and among the Jesuits the superior of a
      house that is a seminary or college.
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WordNet (r) 3.0 (2006):

rector
    n 1: a person authorized to conduct religious worship;
         "clergymen are usually called ministers in Protestant
         churches" [syn: curate, minister of religion,
         minister, parson, pastor, rector]

The Devil's Dictionary (1881-1906):

RECTOR, n.  In the Church of England, the Third Person of the
parochial Trinity, the Cruate and the Vicar being the other two.