重大|じゅうだいjuudai[0]heiban (flat)

1. na-adjective, nounserious; important; significant; grave; weighty
   彼かれは重大じゅうだいな発見はっけんをした。↗

   He made an important discovery.

• Synonym重要じゅうようNeutralIndispensable and weighty, as in 「重要な会議」; fits positive and negative contexts. 「重大」 stresses large impact and grave consequences, as in accidents and responsibility.
• Synonym肝心かんじんNeutralCrucial — points to the indispensable core, as in 「肝心な点」; the emphasis is on what cannot be done without, not on gravity.
• Synonym大事だいじNeutralEveryday word for important or precious things, as in 「大事な物」; also major events. 「重大」 is more formal and carries a graver tone.
• Synonym肝要かんようWrittenWritten/formal prose meaning vitally important, as in 「～が肝要だ」; not an everyday word.
• Synonym深刻しんこくNeutralSerious problems and grim, worsening situations, as in 「深刻な影響」; the emphasis is on how bad things have become.
• Synonym由々しいゆゆしいWrittenWritten/formal prose for a grave, worrying state of affairs, as in 「由々しき事態」.
• SynonymシリアスNeutralLoanword for serious or earnest in tone, as in 「シリアスな話」; mostly describes atmosphere or works such as films and novels.
• Synonym緊要きんようWrittenFormal written word for urgent as well as important, as in 「緊要な課題」.
• Synonym大切たいせつNeutralHere take it as 「大切（たいせつ）」, meaning important and cherished; when read 「おおぎり」 it means cut into large pieces, unrelated to 「重大」.
• Related主要しゅようNeutralMeans principal or dominant, as in 「主要な産業」; concerned with what is primary versus secondary, not with gravity or consequence.
• Related重いおもいNeutralThe plain adjective for heavy; also for heavy responsibility or serious illness, as in 「責任が重い」. Common in colloquial speech.
• Related決定的けっていてきNeutralMeans decisive — able to settle the outcome, as in 「決定的な証拠」; about determining results, not about how serious something is.
• Related大変たいへんNeutralColloquial word for something tremendous, serious or arduous, as in 「大変なことになる」; common in speech and broader than 「重大」.
• Related重篤じゅうとくWrittenMedical term for critical severity, whether of a patient's condition or of side effects, as in 「重篤な副作用」.
• Related枢要すうようWrittenFormal written word for pivotal, hub-like importance; rare in everyday use.
• Antonym軽微けいびWrittenAntonym. Written/formal prose for slight damage or harm, as in 「軽微な事故」; the direct opposite of 「重大」 in degree.
• Antonym些細ささいNeutralAntonym. Means trivial and not worth attention, as in 「些細なこと」; the opposite of 「重大」 in scale.

Use 「重大」 for matters of great consequence with serious fallout, typical of accidents and responsibility. For general importance pick 「重要」 or the everyday 「大事」; for the crucial point 「肝心」; for a worsening situation 「深刻」; for critical illness 「重篤」. 「大変」 and 「重い」 are common in speech, 「シリアス」 covers a serious tone in works, and 「軽微」/「些細」 are the opposites for slight or trivial. Written alternatives: 「肝要」, 「由々しい」, 「緊要」, 「枢要」.

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

1. 重おもくて大おおきいこと。
2. 程度ていどや性質せいしつなどが非常ひじょうに重要じゅうような様子ようす。
3. 事態じたいがただごとでなく、対処たいしょ次第しだいでは失敗しっぱいや死しを招まねきかねない様子ようす。