Silly sienna Share definition Flag Si•lly•si•enn•a- a nickname for a silly girl that’s named sienna. (especially when it’s sienna lewis) A:yo yk that girl sienna B:oh yeah you mean silly siennaA:yeah she’s so silly dude Silly sienna by Mangoflavoedhotsauce August 19, 2021 0 0 Get merch Get the Silly sienna mug. Buy Now — $32.95 See more merch