How to say "legality" in Japanese

• 適法性てきほうせい
  nounLegality as conformity to legal requirements: whether an act, procedure, or decision is permissible under the law. The nuance is compliance with specific rules, so it suits legal and administrative discussion.
• 合法性ごうほうせい
  nounThe straightforward word for legality in the plain sense: whether something is legal or illegal. Use it when asking if an action, measure, or arrangement complies with the law.
• レジティマシー
  nounA katakana loanword that really means 'legitimacy': the rightful standing or acceptability of a government, institution, or rule. Seldom the word you want for legality; reach for it only when 'legitimacy' itself is meant.
• 正当性せいとうせい
  no-adjectiveReally means justification or appropriateness: whether an action, claim, or decision is warranted or proper, whether or not law is involved. For legality in the strict legal sense it is usually not the word.

For the plain question of whether something is legal, use 合法性 (適法性 stresses conformity to specific legal requirements); 「レジティマシー」 and 正当性 are really about legitimacy and justifiability, not legality proper.

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

• 適法性てきほうせいlegality
• 合法性ごうほうせいlawfulness
• レジティマシーlegitimacy
• 正当性せいとうせいlawfulness