Guess Not Share definition Flag Quirky remark made to interupt someone before they answer a question, often causing laughter and lightening the mood.Author: Sarah K. Sarah: Have you seen my keys?Zach: Whe...Sarah: Guess not!Zach: ...re did you put them last? Guess Not by Gorgnad August 18, 2009 0 0 Get merch Get the Guess Not mug. Buy Now — $32.95 See more merch