The innocence and imagination that appears in the hearts of young children. As the children grow older, they become more mature, and gain responsibilities. They lose their muchness.
You used to be much more..."muchier." You've lost your muchness.
A word used to describe a vast amount of something, whether it be an object or an emotion. Commenly used by teenage girls of the slightly strange kind.
"Oh wow I love you very muchness"
"This cake has muchness sugar!!"