Millionairess
/ˌmɪljəˈnerəs/
Definition 1 of 1
Pro Tip 1/3Gender Specific
Used only for women, similar to 'heiress' but emphasizes wealth amount. 
After the inheritance, she became a millionairess.
Pro Tip 2/3Cultural Imagery
Evokes a lavish lifestyle, often seen in movies or literature. 
The millionairess arrived in a chauffeur-driven limousine.
Pro Tip 3/3Rarely Used
Not common in everyday speech, may sound old-fashioned or formal. 
At the gala, everyone was curious about the elusive millionairess.