A woman whose job is to look after passengers on a plane or a ship — bringing food and drinks, showing people to their seats, keeping everyone safe and comfortable. The important thing to know is that the word has aged. It was the normal word for decades, but it names the worker's sex, and nobody's job needs to do that, so English now prefers 'flight attendant' — which covers everyone, and which is what the airlines themselves say. 'Stewardess' still turns up: in older films and books, in the way older people talk, sometimes in shipping. But if a student uses it today, it can sound dated at best, and to some ears a little disrespectful — as if the job were still about a pretty young woman serving drinks rather than about the person who gets you out of a burning aircraft. Use 'flight attendant' and you are safe everywhere. The male form 'steward' still lives on more comfortably on ships and in some other settings, which is a little unfair, but that is how it is.