Consider the term(s) idiotism. It can mean a peculiarity of phrase, or idiom. Or it can mean the condition of lacking intellect, or idiocy. Certainly these are widely disparate senses; and each stems from a unique Greek root. But they do share the element "common", in the pejorative sense.

edit: According to the OED, in the 16th C., instances of the word idiot are found with initial n, transferred from an; nidiot was further popularly corrupted to nidget; cf. the modern vulgar pronunciation, sometimes graphically represented as idget.

the Contrarian

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