Tending to crump; characterized by loud crunching or explosive sounds.
From 'crump' (onomatopoetic verb) plus the adjectival suffix '-y'; originally and primarily a military term from WWI onward.
Military terminology that sounds vivid and onomatopoetic tends to persist in English—'crumpy' survived alongside 'creepy,' 'jumpy,' and 'bumpy' because these '-y' adjectives feel right to English speakers.
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