The Collaborative International Dictionary of English v.0.48:

Preceptor \Pre*cep"tor\, n. [L. praeceptor, fr. praecipere to
   teach: cf. F. pr['e]cepteur. See Precept.]
   1. One who gives commands, or makes rules; specifically, the
      master or principal of a school; a teacher; an instructor.
      [1913 Webster]

   2. The head of a preceptory among the Knights Templars. --Sir
      W. Scott.
      [1913 Webster]

WordNet (r) 3.0 (2006):

preceptor
    n 1: teacher at a university or college (especially at Cambridge
         or Oxford) [syn: preceptor, don]