What is the Meaning of "Yogi"?

Yogi means one who has controlled himself completely, and therefore he is the controller of the whole creation.

Yogi means a person who has complete control over himself, whose senses are completely under his mastery, whose mind is completely ruled by him, and he cannot be ruled by his mind. Such a person becomes the Master of matter, the Master of mind, the Master of the creation, and he is in communion with God.

Yoga has two meanings: on the lower plane it means complete self-conquest, on the higher plane it means complete Union with God.

H.D. Paramahamsa
Omkarananda Saraswati