Other forms: millionaires
A millionaire is someone who has at least a million dollars. If you're a millionaire, you are incredibly wealthy — but not as rich as a billionaire.
In U.S., if you have a million dollars — or things that are worth that much, like a million-dollar house — you're a millionaire. In the U.K., a millionaire has a million pounds. This word describes a specific amount of wealth, but it's also a metaphor for "rich," so you might say, "My neighbors are millionaires — they travel to foreign countries all the time!" The first American millionaire was John Jacob Astor, who earned his riches from 18th-century fur trading.