/ ˈgʊruː; NAmE / noun
1.
a Hindu or Sikh religious teacher or leader
2.
( informal ) a person who is an expert on a particular subject or who is very good at doing sth :
a management / health / fashion, etc. guru
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WORD ORIGIN
from Hindi and Punjabi , from Sanskrit guru weighty, grave (compare with Latin gravis ), hence elder, teacher.