Clairvision does not refer to psychic clairvoyance, but to a state of spontaneous awakening: 'clarity-vision'.
'Clair-vision' implies taking a different standpoint of consciousness, away from the chatter of the ordinary mind. It is a vision of the heart as much as it is a vision of the eye.
Clairvision is akin to the concept of gnosis, as the Gnostics were people who placed more emphasis on direct experience than on belief.
Clairvision is also akin to the Sanskrit veda, 'knowledge', which comes from the root ved, 'to see', 'to cognize'. With Clairvision the purpose isn't to become a clairvoyant but a seer of reality, not unlike the rishis (literally 'seers') who cognized the Vedas.
Another traditional example is found in the writings of Plotinus (3rd century), the founder of Neoplatonism. When asked how the soul could return to a state of unity with the One, Plotinus answered, "Not with a carriage or a boat, but by shutting your eyes and awakening to another level of vision, which is in everyone but which very few ever use." (Enneads 1.6.8)