illicit
/ɪˈlɪsɪt इˈलिसिट्/ adj. (used about an activity or substance) not allowed by law or by the rules of society (कोई गतिविधि या तत्व) क़ानून या समाज के नियमों के विरुद्घ, ग़ैर-क़ानूनी; अवैध
the illicit trade in ivory
They were having an illicit affair.