Synonyms for Extracurricular (same or very similar meaning)
WordNet sense 1 (relating to or being on or near the outer side or limit):
outside
WordNet sense 2 (characterized by adultery):
adulterous, extramarital
WordNet sense 3 (contrary to accepted morality (especially sexual morality) or convention):
illicit
From the ODE community, based on WordNet
add/edit