How to say "stupidity" in Japanese

• 無知むちJLPT N1approx.Common
  noun, na-adjectiveReally means ignorance — not knowing facts — so it covers 'stupidity' only when foolishness stems from lack of knowledge rather than dullness of mind; not the word for calling someone stupid.
  彼かれはすぐに無知むちをさらけ出だした。↗

  He soon betrayed his ignorance.
• 愚ぐCommon
  noun, na-adjectiveDenotes foolishness or folly itself: the silliness or stupidity of a person or an act, rather than mere lack of knowledge. A suitable noun when you want 'foolishness' or 'folly'.
  知しらないほうが幸しあわせな場合ばあいには、知しることは愚ぐである。↗

  Where ignorance is bliss, 'tis folly to be wise.
• 痴呆ちほうCommon
  nounSeldom the word you want for 'stupidity': it really denotes dementia or senility, and used of a person it is a harsh insult ('idiot'). A poor choice for the ordinary sense.

Use 無知 for stupidity as lack of knowledge, 愚 for foolishness or folly as a quality, and avoid 痴呆 for 'stupidity' — it chiefly denotes dementia and insults the person it describes.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 無知むちignorance
• 愚ぐfoolishness
• 烏滸の沙汰おこのさたstupidity
• 鈍才どんさいstupidity
• もの知らずものしらずstupidity
• 魯鈍ろどんimbecility
• 愚劣ぐれつfoolishness
• 不間ぶまclumsiness
• 遅鈍ちどんdullness
• 野暮天やぼてんboorishness
• 守株しゅしゅlack of innovation
• ぽんつくidiot
• うましかidiot
• マジボケ(unintentionally comedic) stupidity
• ぱーfoolishness
• 甘口あまくちstupidity
• 痴呆ちほうstupidity
• 不敏ふびんinability