Ridiculous, silly, or not believable; something that seems made up or nonsensical.
From 'decalcomania,' a transfer printing process popular in the early 1900s. The complex word was shortened and transformed through American slang, eventually meaning something cheap or fake-looking.
This word started as a printing technique (decalcomania) where cheap transfers looked obviously fake—so people started calling ridiculous ideas 'cockamamie' because they seemed as phony as those transfer decorations!
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