A Hindu religious teacher — a man who has given up ordinary life to study and teach, and who has students of his own. The word is a title of respect, and in English it is often used in front of a name, like a title: Swami Vivekananda, Swami Prabhupada. Used that way it works much like 'Reverend' or 'Master' does for other traditions. On its own, as a plain noun, you can say 'he became a swami' or 'the swami spoke for an hour'. In Indian languages the word literally means 'master' or 'lord', and it is used far more widely there than in English — it can address a god, a husband, or any respected man — but English borrowed only the religious-teacher use. Be careful with a second, unkind use: in older English writing and in cartoons, 'swami' sometimes means a fake fortune teller in a turban who claims to read minds, and phrases like 'What am I, a swami?' mean 'How am I supposed to know the future?' That use makes fun of a real religious title, so it is best understood but not copied.