GURU means gu’ actually means darkness while…

GURU means “gu’ actually means darkness while “ru” means light. The two serve as a principle for the development of consciousness where it leads the creation from unreality to reality, from the darkness of ignorance to the light of knowledge. – from ‘UNIVERSAL TRUTH: thinking outside the box’ by Peter C Rogers D.D., PhD

The term Guru is therefore explained as the remover of darkness, who reveals the light of the heart.

See also – https://en.wikipedia.org/wiki/Guru_Gita#cite_note-Grimes1996-5