An adult male who acts like part of the family to is friends' children, and usually the most entertaining adult at any get-together. Derived from friend+uncle
Go play ball with Fruncle Matt. Mommy's getting her drink on.
by LexiCodger December 15, 2011
Adult friend of your family that you've come to thing of as an uncle.
That's my fruncle. He isn't really my uncle but he's been a friend of the family my whole life.
by Serialseb May 24, 2007