Wikipedia
Campaniacum is the etymon inferred from numerous toponyms in France. The Toponymie générale de la France (TGF) derives it from a Roman personal name Campanius and the Gaulish suffix -acum. The -i- (which is important in the phonetic evolution of *Campaniacum) suggests that Campanius is a gens name.
The modern forms differ according to the diverse phonetic evolutions of the local dialects.
- Campagnac (TGF § 7029)
- Campénéac ( Morbihan) (TGF § 7535)
- Campigny (TGF § 8819)
- Champagnac (TGF § 7061 and § 7438)
- Champagnat (TGF § 7612 and § 8480)
- Champagné (TGF § 8133)
- Champagneux (TGF § 8537)
- Champagney (TGF § 7873)
- Champagny (TGF § 8868)
- Champigny (TGF § 8868)
The initial /ka/ of *Campaniacum became /ʃa/ (written Cha) 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 (southern one) /ka/ (written Ca-) was preserved.
The form Champigny is purely French (f. e. : Champigny-sur-Marne is in the Val-de-Marne), because of its [i] between [p] and [ñ]. 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 (fungum) campaniolum ('mushroom') which became champegneul in Old French and champignon (with substitution of suffix) in modern French.