Synonyms for Heathen (same or very similar meaning)
WordNet sense 1 (a person who does not acknowledge your god):
gentile, infidel, paganWordNet sense 2 (not acknowledging the God of Christianity and Judaism and Islam):
ethnic, heathenishWordNet sense 3 (hostile or indifferent to religion):
irreligiousFrom the ODE community, based on WordNetadd/edit