A person whose wealth equals at least one billion dollars, making them extraordinarily rich.
From French 'billion' (one thousand million) + suffix '-aire' (one who has). The word entered English in the 1800s as global wealth increased. 'Million' comes from Latin 'mille' (thousand), and 'billion' adds another 'bi-' (two) for scale—literally 'two million' in some countries.
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