a word defining one's level of intelligence, usually used by an incredibly cool, awesome, and intelligent person.
Sam: god, my geniusness is just so great. who else could have thought of a brilliant plan to get Rachel to stop reading our shit?
Stephanie: you're so right! hey wait a minute, GENIUSNESS IS NOT A WORD!
Sam: of course it's a word. you can add '-ness' to any word and it's a word, trust me. if you don't believe me, go on www.urbandictionary.com in like 4 days and i PROMISE it'll be there.