Whole books are written in the quest to define the art of poetry.
Not a definition as such, but I rather like this, which I came across in Karen Armstrong’s The Great Transformation. She’s talking about the rituals of the Aryan people of the late Vedic period (c. 500 BCE).
When the king arrived back safely from his raid, with the spoils of battle, he had become one with the brahman. He was now the axis, the hub of the wheel that would pull his kingdom together, and enable it to prosper and expand. Brahman was also experienced in silence. A ritual often ended with the brahmodya competition to find a verbal formula that expressed the mystery of the brahman. The challenger asked a difficult and enigmatic question, and his opponent answered in an equally elusive manner. The match continued until one of the contestants was unable to respond: reduced to silence, he was forced to withdraw. The transcendence of the brahman was sensed in the mysterious clash of unanswerable questions that led to a stunning realisation of the impotence of speech. For a few sacred moments, the competitors felt one with the mysterious force that held the whole of life together, and the winner could say that he was the brahman.