鈍|どんdon[1]atamadaka (head-high)

1. na-adjective, noundull; slow; stupid; dull-brained

• SynonymのろいNeutralStresses sluggish movements and slow reactions; far more common in everyday use than 「鈍」. Also used for being indulgent toward the opposite sex.
• SynonymのろまCasualColloquial term for a slow, dim-witted person — slow-moving and lacking wit. Carries mockery or insult; more derogatory than 「鈍」.
• SynonymどんくさいCasualColloquial; stresses slow, unskillful movements and reactions. Often used in self-mockery or to show disdain for someone else.
• Synonym鈍臭いのろくさいCasualThe same word as the entry above, also written 「鈍臭い」; only the spelling differs, the meaning is unchanged.
• SynonymとろいCasualColloquial, with a Kansai-dialect flavor; stresses slow reactions and comprehension. Also said of a weak fire or flame.
• Synonym愚鈍ぐどんWrittenWritten word for stupidity and dullness combined; puts more emphasis than 「鈍」 on a dull mind.
• Synonym遅鈍ちどんWrittenWritten but rare; stresses slow, sluggish movement. Close in meaning to 「鈍」.
• Synonym魯鈍ろどんWrittenWritten word stressing stupidity and dullness; also used as an old medical classification term.
• Synonym鈍重どんじゅうWrittenWritten word for heavy, sluggish movement and a stolid, dull character.
• RelatedアホCasualColloquial insult for a fool, especially common in Kansai; can sound affectionate or mocking depending on tone.
• Related遅いおそいNeutralThe most common everyday word for slow or late; covers low speed or lateness but carries no hint of stupidity.
• RelatedばかCasualThe most common everyday insult, 'stupid' or 'idiot'; broader in range than 「鈍」.
• Related間抜けまぬけCasualColloquial for someone who acts silly or leaves out what matters; carries a mocking tone.
• Related愚ぐWrittenWritten word for foolishness; also a humble first-person pronoun, as in 「愚生」.
• Related愚かおろかWrittenWritten word for foolishness born of poor judgment, as in 「愚かな行為」.
• Related緩慢かんまんWrittenWritten word for slow movement or progress, or lax, sloppy handling; says nothing about the mind.
• Related白痴はくちWrittenThe same word as entry 17, also written 「白痴」; the scolding 「この戯けが」 is typical of period dramas.
• RelatedゆっくりNeutralThe everyday word for 'slowly'; neutral and free of any negative shade, unlike 「鈍」.
• RelatedとんまCasualColloquial — more so than 「鈍」; stresses a dim, goofy air with a comic touch.
• RelatedうすのろCasualColloquial and derogatory; stresses slow reactions and slow comprehension — a half-wit.
• Related痴鈍ちどんWrittenWritten but rare; stresses stupidity and slowness. Synonymous with 「愚鈍」.
• RelatedたわけCasualColloquial but old-fashioned; mainly heard in period dramas as a harsh insult.
• Related愚昧ぐまいWrittenWritten word stressing ignorance and failure to grasp reason, as in 「愚昧な民」.
• Related愚劣ぐれつWrittenWritten word stressing foolish, worthless inferiority, as in 「愚劣な行為」.
• Antonym鋭えいWrittenWritten antonym: sharp and keen, as in 「鋭利」 — the direct opposite of dull 「鈍」.
• Antonym敏びんWrittenWritten antonym: quick and alert, as in 「機敏」 — the opposite of dull 「鈍」.

For dull reactions, a slow mind or a blunt blade, 「鈍」 itself appears mostly in written compounds such as 「鈍感」「鈍器」; in speech say 「鈍い」 or 「鈍感」. For everyday slowness use 「遅い」 or 「のろい」, and for clumsy slowness 「鈍くさい」. The Sino-Japanese words 愚鈍, 遅鈍, 魯鈍, 鈍重 and 緩慢 belong to formal prose, while のろま, アホ, ばか, まぬけ and the like are spoken insults ranging from teasing to harsh. ゆっくり is a neutral 'slowly' with no negative shade.

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

1. 刃物はものや感覚かんかくが鋭するどくなく、反応はんのうや理解りかいが遅おそいさま。