Oxford defines “Guru” as the following, (Hinduism and Buddhism) a spiritual teacher, especially one who imparts initiation, from Hindi and Punjabi, from Sanskrit guru ‘weighty, grave’ (compare with Latin gravis ), hence ‘elder, teacher’.
My dog Pika, aka The Pi, was my Guru. Aged before her time, with flecks of grey hair on her face even as a young dog, The Pi often embodied a stern expression with absolutely no tolerance for fools of any species. So how She chose me to impart Her Wisdom and Lessons I have no idea, other than, like me, She embraced a “soul/student” who lacked the ability to see their own hidden Divine Potential.