How to say "deadly" in Japanese

• 必殺ひっさつCommon
  no-adjectiveCovers 'deadly' only for attacks: a blow or strike that brings certain death. It belongs to combat and martial-arts contexts, describing a lethal or knockout blow rather than deadly things in general.
• 命取りいのちとりCommon
  no-adjectiveCovers 'deadly' as fatal or mortal: something that proves fatal or costs a life. Typical contexts are injuries, illnesses or blunders — an oversight that turns out to be deadly.
  その間違まちがいが彼かれの命取いのちとりとなった。↗

  The mistake cost him his head.

Use 必殺 for deadly force in combat — a blow or attack that brings certain death — and 「命取り」 for anything fatal, an injury or blunder that costs someone their life.

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

• 必殺ひっさつbringing certain death
• 命取りいのちとりfatal
• 殺人的さつじんてきhorrible
• 致死的ちしてきlethal