Metaplasm

A metaplasm is a change in the orthography (and hence phonology) of a word. Originally it referred to techniques used in Ancient Greek and Latin poetry, or processes in those languages' grammar.

Many poetic metaplasms are useful for describing processes in the natural development of languages:

In rhetoric, metaplasm is the modification of word order for emphasis.

In the grammar of the Romance languages, metaplasm refers to the change in the grammatical gender of nouns from their original gender in Latin.