Seriishly Share definition Flag adv. (pronounced seer-EE-ish-lee) Sort of seriously (used almost exclusively in the context of relationships). I'm having trouble sleeping with other women because I'm seriishly into this one. Seriishly by Cobra Baghdad April 8, 2009 0 0 Get merch Get the Seriishly mug. Buy Now — $32.95 See more merch