Here are some definitions:
a person who seeks by contemplation and self-surrender to obtain unity with or absorption into the Deity or the absolute, or who believes in the spiritual apprehension of truths that are beyond the intellect.
noun. a person who claims to attain, or believes in the possibility of attaining, insight into mysteries transcending ordinary human knowledge, as by direct communication with the divine or immediate intuition in a state of spiritual ecstasy.
Paul says it this way —
But he who is joined to the Lord is one spirit with Him.
1 Corinthians 6:17