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Synonyms for Arduous (same or very similar meaning)

WordNet sense 1 (taxing to the utmost; testing powers of endurance):
strenuous, straining

WordNet sense 2 (characterized by toilsome effort to the point of exhaustion; especially physical effort):
backbreaking, grueling, gruelling, heavy, laborious, punishing, toilsome, operose

WordNet sense 3 (not easy; requiring great physical or mental effort to accomplish or comprehend or endure):
difficult, hard

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