Definition - A process of language change where a word comes to have a more negative meaning.

Example -
In Old English the word silly meant "blessed" or "holy." In Modern English it means "foolish."

Etymology -
The word derives via French from the Latin pejor, worse.

Oxford English Dictionary -
Its first citation in this sense is from 1889:
"Their [sc. words'] degeneration (technically termed pejoration;…) is often due to a selection and specialization of some ethically lower connotation which may be implied in them."
(As quoted from the Century Dictionary, 1939: L. H. Gray, Foundations of Language, ix. 259 )

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