adulterous
extracurricular
extramarital
illegal
unlawful
actionable
against the law
anarchic
anarchistic
anomic
back-door
banned
barred
black-market
bootleg
chargeable
clandestine
contraband
contrary to law
criminal
felonious
flawed
forbade
forbid
forbidden
freeloving
furtive
illegitimate
impermissible
improper
incestuous
irregular
justiciable
lawless
nonconstitutional
nonlegal
nonlicit
nonpermissible
not permitted
off limits
out of bounds
outlaw
outlawed
prohibited
punishable
ruled out
secret
sneaky
carnal
consensual
dishonorable
heterosexual
legitimate
lucrative
nefarious
overseas
recreational
sexual
sinful
unauthorized
unethical
unholy
complicit
explicit
implicit