Guru
WordNet
noun
(1) A Hindu or Buddhist religious leader and spiritual teacher
(2) A recognized leader in some field or of some movement
"A guru of genomics"
(3) Each of the first ten leaders of the Sikh religion
WiktionaryText
Etymology
From / < , originally "heavy" and in this sense cognate to English .
A traditional etymology based on the Advayataraka Upanishad (14–18, verse 5) describes the syllables gu 'darkness' and ru 'dispeller', combining as who dispells darkness.