To groan or rumble (archaic or dialectal term, rarely used in modern English).
Of Germanic origin, possibly related to Middle High German 'grotzen' or dialectal Northern European words for groaning sounds. The -en ending suggests Germanic verb formation.
Grotzen is a word that barely survives in English—it's mostly disappeared, but it shows us how onomatopoetic words (words that sound like what they mean) develop in Germanic languages!
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