Campaniacum

Campaniacum is the etymon inferred from numerous toponyms in France. The Toponymie générale de la France derives it from a Roman personal name Campanius and the Gaulish suffix -acum. The -i- suggests that Campanius is a gens name.
The modern forms differ according to the diverse phonetic evolutions of the local dialects.

The initial /ka/ of *Campaniacum became /ʃa/ in most of Gaul, both in langue d'oïl dialects and the northern langue d'oc dialects; but north of the Joret line, and most Langue d'oc dialects /ka/ was preserved.
In the form Champigny, Gaston Zink offered an explanation for the sequence ign in place of the expected agn: before the palatal consonant /ɲ/, the /a/ shifted to /e/, which in turn closed to /i/; Zink points out the parallel form campaniolum which became champegneul in Old French and champignon in modern French. This shift is restricted to central langue d'oïl.