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1.
A person who has become wealthy exclusively through inheritance, rather than work or other means. Such a person has received or will receive their millions, or even billions as a beneficiary of a last will and testament.
There are self-made men, and then there are willionaires; the people who have all the money, but did none of the work.
by Keyser Tomasi July 26, 2009
 
2.
Someone who acts, thinks, and pretends to be a millionaire, but they are not. As wanksta is to gangsta.
This person generally will display lots of monopoly style money around their person, hoping that this will encourage more real money.
Did you see that willionaire flashing all of Uncle Pennybag's (the guy from monopoly) money around? Too bad they didn't pass go!
by Ghetto Fabulous Wanksta August 31, 2005