WordNet sense 1 (not conforming to legality, moral law, or social convention):

improper, unconventional

WordNet sense 2 (contrary to rule or accepted order or general practice):

irregular

WordNet sense 3 (contrary to accepted morality (especially sexual morality) or convention):

illicit

WordNet sense 4 (of marriages and offspring; not recognized as lawful):

illegitimate

WordNet sense 5 (contrary to or forbidden by law):

outlawed

WordNet sense 6 (prohibited by law or by official or accepted rules):

illegal

WordNet sense 7 (unlawfully violating the rights of others):

wrongful

WordNet sense 8 (disobedient to or defiant of law):

outlaw