What is the term for the complete change in meaning of a word?

The term that describes a complete change in meaning of a word is referred to as a semantic shift. This occurs when a word evolves in meaning over time, often leading to a significant alteration of its original definition. For example, the word "silly" originally meant "happy" or "fortunate," but it has undergone a semantic shift to primarily mean "lacking in good sense" in contemporary usage.

Understanding semantic shift is vital in the study of language, as it reflects how cultural and societal changes influence language development. This term encapsulates both minor nuances and substantial redefinitions, highlighting the dynamic nature of language. Other choices address related but distinct concepts: connotation pertains to the additional meanings or associations a word may carry beyond its literal definition, neologism refers to the creation of a new word or expression, and deterioration describes a decline in meaning or quality but does not encompass the complete transformation implied by a semantic shift.