illicit

adj

1. Not approved by law, but not invalid.

   “The bigamous marriage, while illicit, was not invalid.”

   “Such migrants may violate our laws against illicit entry, but if that's all they do then they are trespassers, not criminals.”

2. Breaking social norms.

   “I only can properly enjoy carol services if I am having an illicit affair with someone in the congregation.”

3. Unlawful.

   “Ayşe Erkoç learned long ago that the secret of doing anything illicit in Istanbul is to do it in full public gaze in the clear light of day. No one ever questions the legitimacy of the blatant.”

noun

1. A banned or unlawful item.

   “A large number of studies, however, have reported that it is rare for the user of 'hard' drugs not to have initiated cannabis use prior to the other illicits.”