A vertical aerodynamic fin called the Merkin first saw its use in Formula One on the Williams FW22A (2000) (as named by Chief Aerodynamicist Geoff Willis), although this name was changed to the more common name of "Forward Guide Vane" after higher authorities found out its true meaning.
"Merkin" is also used to refer to a male sex-toy in the humorous novels of Tom Sharpe. Both the Shorter Oxford English Dictionary and The Joy of Sex define the Merkin as an "artificial vagina."[4]
In gay slang, "merkin" may refer to a man who acts as the date for, or even marries, a lesbian — usually for the purpose of making her appear heterosexual for various social reasons.[5] It is a humorous variant on the term "beard", meaning a false date or romantic partner designed to mislead others about the nature of a relationship, and/or to conceal someone's sexual orientation.
Wikipedia suggests these as alternate definitions.