See laborious in Webster's New World Roget's A-Z Thesaurus II
adjective
Requiring great or extreme bodily, mental, or spiritual strength:
arduous, backbreaking, burdensome, demanding, difficult, effortful, exacting, exigent, formidable, hard, heavy, onerous, oppressive, rigorous, rough, severe, taxing, tough, trying, weighty. See heavyNot easy to do, achieve, or master:
arduous, difficult, hard, serious, tall, tough, uphill. See easy
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