Superlative form of billowy; the most characterized by billows or the greatest in wave-like motion and surge.
From 'billowy' plus the superlative suffix '-est,' with the base 'billow' from Old Norse 'bylgja,' which has roots possibly relating to 'belly' (swelling).
Billowiest is so specific and poetic that it's almost never used in everyday speech—it's the kind of word Romantic poets loved for its evocative, undulating sound.
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