The Greek epoptes (Strong's G2029) means 'eyewitness,' 'one who has seen,' or 'overseer.' It combines epi (upon) and optes (one who sees). In the ancient world, it also referred to an initiate in mystery religions who had achieved the highest level of insight — one admitted to the inner seeing. In the New Testament, Peter uses it specifically of his direct eyewitness experience of the Transfiguration.
Peter's claim to be an epoptes — an eyewitness — of Christ's majesty (2 Peter 1:16) is one of the strongest apostolic assertions in the New Testament. He is explicitly countering 'cleverly devised myths' with the testimony of direct, personal observation. He did not receive a vision, a tradition, or an interpretation — he was there on the holy mountain and heard the voice from heaven. This epistemological claim is foundational to Christianity: the gospel is grounded in historical witness, not mystical speculation. The Transfiguration confirmed the prophetic word and the identity of Jesus. Peter saw, heard, and testified — and his testimony remains trustworthy.