How to say "conclusive" in Japanese

• 断固だんこCommon
  taru-adjective, adverb (with と)Covers the 'resolute, firm' side of the gloss: an unwavering attitude or stance, as when refusing or opposing something outright. It is seldom the word you want for 'conclusive' evidence or proof.
  私は家いえにとどまるようにと彼かれらに懸命けんめいに言いったが、彼かれらは断固だんことして私の意見いけんに耳みみを傾かたむけようとはしなかった。↗

  I tried hard to make them stay home, but they refused to listen to me.
• 決定的けっていてきCommon
  na-adjectiveThe usual choice for 'conclusive' in the sense of evidence, proof, or a factor that settles a question once and for all; it also covers the 'decisive' and 'definite, final' senses.
  きっと無罪むざいになるだけの決定的けっていてき切り札きりふだを隠し持かくしもっているに違ちがいない。↗

  I'm sure he has something up his sleeve.

For 'conclusive' meaning evidence or proof that settles a question, 決定的 is the word to reach for; 断固 instead expresses a firm, resolute attitude and is rarely the right rendering of 'conclusive' itself.

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

• 断固だんこfirm
• 決定的けっていてきdefinite