Source : Webster's Revised Unabridged Dictionary (1913)

Mentor \Men"tor\, n. [From Mentor, the counselor of Telemachus,
   Gr. ?, prop., counselor. Cf. {Monitor}.]
   A wise and faithful counselor or monitor.

Source : WordNet®

mentor
     n : a wise and trusted guide and advisor [syn: {wise man}]
     v : serve as a teacher or trusted counselor; "The famous
         professor mentored him during his years in graduate
         school"; "She is a fine lecturer but she doesn't like
         mentoring"

Source : Free On-Line Dictionary of Computing

MENTOR
     
        CAI language.  "Computer Systems for Teaching Complex
        Concepts", Report 1742, BBN, Mar 1969.