1. A pubic wig
2. A derogatory term used to describe a person who tries to conceal her lascivious tendencies.
Etymology: First used in around 1617, a merkin was a pubic wig prostitutes used to hide syphilis marks or genitals that were shaved in order to kill lice. Merkins are currently used by topless dancers and actresses to prevent full-frontal exposure.
Use: Have you read Paris Hilton's new autobiography, My Life as a Merkin.