decuman

/ˈdɛkjʊmən/
adjective
  1. Very large or powerful, especially referring to a wave; huge, monstrous.
    • A decuman swell rose suddenly, crashing against the cliffs with tremendous force.
    • The sailors braced for a decuman wave that towered over the ship.
    • Ancient stories often describe decuman storms that could swallow entire fleets.
Antonyms
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