“Impertinent” looks as if it ought to mean the opposite of “pertinent,” and indeed it once did; but for centuries now its meaning in ordinary speech has been narrowed to “impudent,” specifically in regard to actions or speech toward someone regarded as socially superior. Only snobs and very old-fashioned people use “impertinent” correctly; most people would be well advised to forget it and use “irrelevant” instead to mean the opposite of “pertinent.”
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