To concoct is to create or prepare something by mixing various ingredients or ideas. It is often used for cooking mixtures or for inventing stories or plans, sometimes in a sneaky way.
From Latin 'concoquere', meaning 'to cook together, digest', from 'com-' and 'coquere' ('to cook'). The sense broadened from literal cooking to mixing and inventing.
The word started in the kitchen but wandered into the world of imagination: you can concoct a soup or a crazy excuse. Both involve tossing bits together and 'cooking' them until they seem like one believable whole.
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