Lexical change encompasses two distinct phenomena. The first involves changes in the semantic structure or meaning of the signifier, the area traditionally known as semantic change. Lexical change also includes the demise of lexical items with the passage of time, as well as the addition and incorporation of new vocabulary into the lexicon. Most neologisms result from inter-linguistic borrowing or from processes of internal derivational morphology. As borrowings and derivational processes are treated elsewhere in this work, I shall limit this presentation of lexical change in the Romance languages to issues in semantic change (at the level of the individual word) and lexical loss. However, the creation of new lexical items through processes of derivational morphology and through borrowings from other languages has implications for a description of the historical processes of semantic change (especially if viewed from an onomasiological perspective) as well as of lexical loss.

The analysis of semantic change differs from the study of change at other levels. Phonological and morphological change involve dealing at any given moment with a finite number of basic units (phonemes, inflectional and derivational morphemes). Phonological and morphological change essentially lead to the loss or addition of phonemes or morphemes. In contrast, semantic change deals with an infinite number of elements (words) and an infinite number of semantic features (meanings). The acquisition by a word of a new meaning often (perhaps usually) does not entail the (immediate) loss of its earlier meaning(s).