μωρῷ, [6 verses](adj sg masc dat) "Foolish" is moros , which means "dull," "stupid," "sluggish," 'insipid," "blind," and "folly." -- The Greek word translated as "fool" means "dull" and "stupid." This Greek word is the basis for the English word "moron," which technically means a mild mental disability. There is no "thou," that is, no second person pronoun here. It seems to be added to make the context of name-calling clearer. The form of the word can only be that which indicates someone being called by this word.