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2.
a man who has an ongoing affair with another person outside of a relationship in return for financial support from this person, a male mistress
"his girlfriend suspected he was a misteress to another woman when she surprised him at work to thank him for her new bling only to find out he had been fired months previously."

"he found out that his mistress was actually a misteress in a very unpleasant fashion"
by burkielicious February 15, 2007
 
1.
A man other than her husband with whom a married woman has an ongoing sexual relationship.
Damn girl, you married and still got friends with benefits!
Yeah, I've got a few misteresses.
by Dr. L1 April 24, 2008