Sahib is an old respectful way to speak to, or about, a man with power — especially a British or European man in India in the time of British rule. It sits a little like sir: people said it after a name, or used it alone to mean that man in charge. You will meet it in history and in old stories, not in everyday English in most countries. Though actually, in parts of India and Pakistan people still use sahib as a polite word for a man, so it did not wholly die. A European woman in that old world was sometimes called memsahib. The word travelled a long way: into English from Hindustani, where it meant “lord”, and before that from Persian, and before that from Arabic, where it meant “companion”.