A millionairess is a woman with at least a million pounds or dollars. The money-meaning is the same as millionaire; the extra ending only marks that the person is female. Though actually, many people now just say millionaire for a woman as well. Millionairess is not rude, but it can sound like an old film or an old newspaper. Young speakers seldom need it.

女百萬富翁。現在較常直接說 millionaire，不特別標女性。