Guru

Concise Oxford English Dictionary © 2008 Oxford University Press:
guru /ˈgʊruː, ˈguːruː/

▶noun

• 1 a Hindu spiritual teacher.

• 2 each of the ten first leaders of the Sikh religion.

• 3 an influential teacher or expert: a management guru.

– origin from Hindi and Punjabi, from Sanskrit guru ‘weighty, grave’ (cf. L. gravis), hence ‘elder, teacher’.