A Dictionary of Linguistics and Phonetics David Crystal

purism (n.) A term used pejoratively in linguistics to characterize a school
of thought which sees a language as needing preservation from the external
processes which might infiltrate it and thus make it change, e.g. the pressures
exercised by other dialects and languages (as in loan words) and the variations
introduced by colloquial speech. This purist concern is considered misplaced
by linguists, who point to the inevitability of language change, as a reflex
of social, cultural and psychological development.
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