Millionaire

google

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early 19th century: from French millionnaire, from million (see million).

wiktionary

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Borrowed from French millionnaire. Reanalyzable as million +‎ -aire.

etymonline

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millionaire (n.)

"a person worth a million dollars, pounds, francs, etc.," 1821, from French millionnaire (1762); see million. The first in America is said to have been John Jacob Astor (1763-1848).