From: Middle English mistik, from Latin mysticus of mysteries, from Greek mystikos, from mystes initiate
Date: 14th century
2 of or relating to mysteries or esoteric rites: occult
4a: mysterious b: obscure, enigmatic c: inducing a feeling of awe or wonder d: having magical properties
Hexham's Concise Dictionary of Religion
A mystic is one who claims to know god immediately through a form of spiritual inwardness, as against knowing through sensation or through logical processes. They may report the experience of a sacred-human relationship, particularly of a oneness with a divine or trans-divine being or state.
Mystic is a word that has acquired much baggage, often associated with pseudo-science, magic, and the occult. Divorced of these exotic inferences, the mystic simply believes that there exists a reality beyond the material plane of ruled by mathematics and physics. The mystic accesses these realities through "peak experiences," or moments of transcendence. Just as light exists as both wave and particle, the mystic believes that humans can exist in both the physical and the spiritual world simultaneously.
By including one’s perception to all realms of consciousness, the mystic opens themselves up to all fields of possibility. A common conception in Eastern thinking, the mystic pursues an egoless existence, seen as the route to authenticity, wholeness, and intuitive knowledge. The Western construct tends to connect the mystic with a deity, or some absolute divinity.
Atheist Definition: The mystic believes in a reality beyond the physical plane of human sensory perception, and through peak experiences senses this mysterious existence, transcending culturally imposed beliefs and conceptions. The atheist mystic connects intuitively with this alternate reality, becoming more authentic and whole.