Synonyms for Herculean (same or very similar meaning)
WordNet sense 1 (displaying superhuman strength or power):
powerfulWordNet sense 2 (above or beyond the human or demanding more than human power or endurance):
superhumanWordNet sense 3 (not easy; requiring great physical or mental effort to accomplish or comprehend or endure):
hardFrom the ODE community, based on WordNetadd/edit