The Collaborative International Dictionary of English v.0.48:
Gooroo \Goo*roo"\, Guru \Gu*ru"\ (g[=oo]*r[=oo]"), n. [Hind.
gur[=u] a spiritual parent or teacher, Skr. guru heavy,
noble, venerable, teacher. Cf. Grief.]
1. A spiritual teacher, guide, or confessor among the Hindus;
a guru. --Malcom.
2. (g[=oo]"r[=oo]) one who has expert knowledge of a
technical area and serves as an advisor to others; an
expert and teacher. Usually written guru.
3. (g[=oo]"r[=oo]) an intellectual or spiritual guide or
advisor; a mentor. Usually written guru.