noun
legality; lawfulness; legitimacy
Refers to the quality of being in accordance with the law; used in legal, administrative, and formal contexts.
その契約の適法性が裁判で争われた。
The legality of the contract was disputed in court.
新
I consulted a lawyer about the lawfulness of the new regulation.
違法性 is the antonym, meaning illegality or unlawfulness.
Compound of 適法 (tekihō, 'legal, lawful') + 性 (-sei, '-ness, -ity'). The exact historical derivation is straightforward; the term is a modern legal coinage.