To crush something into wrinkles and folds, or to collapse or fall down completely.
From Middle Dutch 'krompelen' or German 'krümmel,' imitative words that sound like the action of crushing and wrinkling. The '-le' ending intensifies the repeated, crumpling motion.
The verb 'crumple' is onomatopoetic at heart—if you say it out loud while actually crumpling paper, your mouth and tongue positions literally mimic the breaking and folding of the paper, which is why onomatopoeia feels so satisfying.
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