Past tense of clump; formed into thick, compact groups or lumps, or walked heavily with dull thuds.
From clump (possibly from Low German klump meaning block or lump). The verb developed in the 17th-18th centuries with both meanings of gathering into lumps and walking noisily.
The word 'clump' beautifully captures the sound and action simultaneously—it's one of those onomatopoetic words that actually sounds like what it describes, so saying 'clump' is almost like hearing footsteps.
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