noun, na-adjective, noun which may take the genitive case particle 'no'
ordinary and ignorant; mediocre and stupid
A strong, literary insult describing someone as both unremarkable and foolish. Rare in everyday speech; mostly found in formal or written criticism.
彼の意見は凡庸愚昧で、聞くに値しない。
His opinion is mediocre and stupid, not worth listening to.
凡庸愚昧な人間には、この芸術の価値はわからないだろう。
An ordinary and ignorant person probably wouldn't understand the value of this art.
A compound of 凡庸 (mediocre, ordinary) and 愚昧 (foolish, ignorant). The exact historical derivation is uncertain, but the combination intensifies the negative assessment.