The classification of disparate entities into categories, not always for the right reason(noun)
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Use "pigeonholing" in a sentence
"Given that I realize most Americans are not, in fact, libertarians, this sort of rhetorical pigeonholing is a bit unsettling."
"Such are the hazards of "pigeonholing" people instead of viewing them as individuals."
"Finch, however, worries that that kind of pigeonholing won't go down well with polka fans, who he says are already fed up with all the lederhosen and accordion jokes they must endure."