noun
illegality; unlawfulness
Primarily a legal term referring to the quality or state of being illegal. Often used in formal contexts such as law, contracts, and official discussions.
その行為の違法性が裁判で争われた。
The illegality of the act was disputed in court.
契約の違法性を指摘する。
Point out the unlawfulness of the contract.
不法 also means 'illegal' or 'unlawful', but is often used in broader contexts (e.g., 不法侵入 'trespassing'). 違法性 is more abstract and formal.
Compound of 違法 (illegal) + 性 (-ness, -ity). The suffix 性 is commonly used to form abstract nouns indicating a quality or property.