How to say "lawful" in Japanese

• 合法ごうほうCommon
  na-adjective, no-adjectiveThe usual word for 'lawful' in the plain sense of permitted by law and not illegal; use it when the question is whether an action or thing is legal or illegal.
  その議論ぎろんに関かんする討論とうろんは合法ごうほうであるようだ。↗

  A discussion of the proposal seems to be in order.
• 適法てきほうCommon
  na-adjective, no-adjectiveAlso 'legal, lawful', but it stresses conformity to legal requirements — whether a procedure or action was carried out lawfully — and is typical of legal and official discussion.
• 合法的ごうほうてきCommon
  na-adjectiveThe adjectival derivative of 合法 with the same core meaning; it characterizes conduct or means as staying within the law — done legally rather than illegally — and can shade into 'law-abiding'.
  あなたは合法的ごうほうてき手段しゅだんで行動こうどうする方ほうがよい。↗

  It is better for you to act by legal means.
• 正当せいとうJLPT N1approx.Common
  na-adjective, nounCovers 'lawful' in the sense of rightful, legitimate and justifiable — a claim, reason or action having proper grounds — where the issue is justification rather than mere legality.
  先生せんせいは彼女かのじょに正当せいとうな取り扱とりあつかいをしなかった。↗

  The teacher didn't do her justice.
• 正しいただしいJLPT N4approx.Common
  i-adjectiveMeans 'right, correct, proper' in a general sense; it fits 'lawful' only when the point is moral rightness rather than legality, and is seldom the word you want for strictly legal senses.

For 'lawful' as 'not illegal' use 合法, with 適法 stressing conformity to legal requirements; 合法的 describes conduct done legally; 正当 covers the 'rightful, justified' sense; 「正しい」 only when 'lawful' means morally right.

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

• 合法ごうほうlegal
• 適法てきほうlegal
• 合法的ごうほうてきlegal
• 正当せいとうjust
• ローフルlawful
• 立派りっぱlegal
• 正しいただしいproper