loon Share definition Flag A Psychotic person. Short for lunatic. Damn that guy was chewing on his finger because he thought it was a peice of chicken. What a fucking LOON! loon by Delta9 May 13, 2005 Words you can keep railfan mug chonk mug chud mug based mug 67 mug slime mug mogging mug chopped mug thot mug glazing mug huzz mug yams mug larp mug unc mug cracked mug simp mug baddie mug bop mug lolcow mug