Translation guide
Describes someone who is slow to understand, not sharp, or lacking intelligence. Japanese has several common words and phrases to express this, ranging from blunt to softer, indirect expressions.
To describe a person who takes time to grasp things or is generally not bright.
Common word meaning 'slow', 'dull', or 'obtuse'. Can refer to physical slowness or mental dullness.
彼は頭の回転が鈍い。
He is slow on the uptake.
Means 'stupid', 'idiotic', or 'dull-witted'. More insulting than 鈍い. Often used for someone who makes foolish mistakes.
そんな間抜けなミスをするなんて。
How could you make such a dumb mistake?
Formal/literary term meaning 'stupid' or 'dull-witted'. Stronger and more serious than 鈍い.
彼は愚鈍な男だ。
He is a dull-witted man.
To bluntly say someone is not smart, often in a derogatory way.
The most common word for 'stupid' or 'fool'. Can be used playfully or seriously. Very versatile.
彼は本当に馬鹿だ。
He is really stupid.
Kansai dialect equivalent of 馬鹿, but widely understood. Often used jokingly.
あほなこと言うな。
Don't say stupid things.
Means 'low intelligence' or 'feeble-minded'. Harsh and clinical, often used as an insult.
To emphasize that someone is stubbornly slow to understand or insensitive.
Literally 'head is hard'. Means inflexible thinking, stubborn, or slow to accept new ideas. Not necessarily low intelligence, but rigid.
彼は頭が固くて話にならない。
He's so thick-headed, you can't reason with him.
Means 'slow to understand' or 'obtuse'. More about comprehension than stubbornness.
物分かりの悪い生徒だ。
He is a slow-witted student.
Means 'insensitive' or 'thick-skinned'. Often used for emotional dullness, but can imply mental slowness.
To refer to intellectual disability or severe slowness, often in clinical or euphemistic contexts.
Standard term for 'intellectual disability'. Neutral and appropriate in formal contexts.
彼は知的障害がある。
He has an intellectual disability.
Short for 精神遅滞 (intellectual disability), but can be used alone to mean 'retardation'. Often considered outdated or offensive; use with caution.
Can be offensive if used casually. Prefer 知的障害 in formal settings.
Means 'slowpoke' or 'dimwit'. Very casual and derogatory. Not clinical.
のろまな奴だな。
What a slowpoke.
English 'dull-witted' does not have a single perfect equivalent. Using 鈍い alone may be too vague; often you need a phrase like 頭の回転が鈍い to clarify mental slowness.
馬鹿 is standard Japanese, while 阿呆 is Kansai dialect. Both mean 'stupid', but 阿呆 can sound softer or more playful depending on region. In Kanto, 馬鹿 is more common; in Kansai, 阿呆 is preferred.
低能な奴だ。
What a dimwit.
彼は鈍感で、人の気持ちがわからない。
He is so dense, he doesn't understand people's feelings.
彼は精神の発達に遅れがある。
He has a developmental delay.