Superlative form of crumbly: most crumbly.(adjective)
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Use "crumbliest" in a sentence
"She selected from the brown jar on the table three of the brownest, crumbliest, most perfect cookies, with a walnut meat perched atop of each, placed them temptingly on the saucer and, descending the steps, came swiftly across the grass to the triumphant"
"She selected from the brown jar on the table three of the brownest, crumbliest, most perfect cookies, with"
"The Flake has a history of sensual advertising, dating back to 1959, with the continuing jingle line, "Only the crumbliest, flakiest chocolate, tastes like chocolate never tasted before.""