See exigent in Webster's New World Roget's A-Z Thesaurus II
adjective
Compelling immediate attention:
burning, crying, dire, emergent, imperative, instant, pressing, urgent. See bigRequiring great or extreme bodily, mental, or spiritual strength:
arduous, backbreaking, burdensome, demanding, difficult, effortful, exacting, formidable, hard, heavy, laborious, onerous, oppressive, rigorous, rough, severe, taxing, tough, trying, weighty. See heavy
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