Synonyms and Antonyms of formidable
- a formidable, irascible old man who frightened the neighborhood children
- running a marathon is a formidable undertaking
arduous, Augean, backbreaking, challenging, demanding, difficult, effortful, exacting, grueling (or gruelling), hard, heavy, hellacious, herculean, killer, laborious, moiling, murderous, pick-and-shovel, rigorous, rough, rugged, severe, stiff, strenuous, sweaty, tall, testing, toilsome, tough, uphill
abstract, abstruse, complex, complicated, elusive, hairy, insoluble, intricate, involved, knotty, opaque, problematic (also problematical), recondite, serious, spiny, stubborn, thorny, ticklish, tricky
Seen and Heard
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