Past tense of clop; made the sound of a horse's hooves hitting the ground.
From 'clop,' an onomatopoeia imitating the sound of a horse's hooves; possibly related to 'clap' and 'clip,' all sound-imitating words.
Before cars, English speakers needed rich vocabulary for horse sounds—'clopp,' 'clop,' 'clopped' let people paint vivid pictures of horses without saying they were approaching.
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