FOOLISH

愚　グ　おろ（か）

JY f1766 2834
foolish, stupid, ignorant
愚人・ぐじん・fool
愚劣な・ぐれつな・stupid, foolish
humble
愚問・ぐもん・silly question
INDEPENDENT
愚な・ぐな・foolish, silly stupid
KUN
愚かさ・おろかさ・foolishness, stupidity
愚かしい・おろかしい・foolish, stupid, dull

"heart/feelings" together with "clawless scorpion with twisting tail" where the idea of twisting led to convoluted and hence "obscure/not clear".  Therefore this Kanji acquired the sense of unclear feelings and hence irrationality and finally foolishness.

TEST
fool
stupid, foolish
sillyquestion
foolish, silly, stupid
foolishness, stupidity
foolish, stupid, dull