Clues for the word "UNK"

We've had 6 crossword clues used for this word, and seen it 5 times in crosswords. It was last seen in Washington Post Classic crossword on December 24, 2017.

Referring Clues

Pop's bro, slangily
Anonymous: Abbr.
Snuffy Smith, to Jughaid
Teddy, to John Jr.
Mom's bro
Your ol' dad's bro

Last Seen In

Washington Post Classic - December 24, 2017
Pat Sajack's Code Letter - September 06, 2017
USA Today - March 24, 2016
New York Times - April 01, 2012
Wall Street Journal - November 12, 2010