guru

Short definition from Wiktionary

Noun

1. 1
   In Indian traditions: a spiritual teacher who transmits knowledge to a shishya.
2. 2
   Any general teacher (as a term of respect).
3. 3
   An influential advisor or mentor.
4. 4
   A fraudster or conman relying on a projected air of confidence in an obscure field.

Verb

1. 1
   To act as a guru; to give wise advice