River Mermaid Share definition Flag A slut or promiscuous person, esp. flirtatious young women who reside at cottages/cabins during summertime. "Man, your neighbor is hot!" "Oh, Zyn? Yeah, she's a total river mermaid." River Mermaid by panicmania April 18, 2013 0 0 Get merch Get the River Mermaid mug. Buy Now — $32.95 See more merch