One who has achieved self-mastery. Also, a respectful term of address for one's guru (q.v.).
Paramahansa Yogananda has pointed out that "the distinguishing qualifications of a master are not physical but spiritual... Proof that one is a master is supplied only by the ability to enter at will the breathless state (savikalpa samadhi) and by the attainment of immutable bliss (nirvikalpa samadhi)" See samadhi.
Paramahansaji further states: "All scriptures proclaim that the Lord created man in His omnipotent image. Control over the universe appears to be supernatural, but in truth such power is inherent and natural in everyone who attains 'right remembrance' of his divine origin. Men of God-realization...are devoid of the ego-principle (ahamkara) and its uprisings of personal desires; the actions of true masters are in effortless conformity with rita, natural righteousness. In Emerson's words, all great ones become 'not virtuous, but Virtue; then is the end of the creation answered, and God is well pleased.”