Norman toponymy

Place-names in Normandy have a variety of origins. Some belong to the common heritage of the Langue d'oïl extension zone in northern France and Belgium; this is called "Pre-Normanic". Others contain Old Norse and Old English male names and toponymic appellatives. These intermingle with Romance male names and place-name elements to create a very specific superstratum, typical of Normandy within the extension zone of the Langue d'oïl. These are sometimes called "Normanic".

There are still a significant number of Celtic (Gaulish) names, as there are throughout France and western Europe. These names, partly mixed with Latin elements, follow the Late Latin phonetic changes that led to Langue d'oïl.

Almost all the main cities kept a Romanized Celtic name, that produced the modern toponym.

In the following examples, a Gaulish toponym was replaced by the name of the local tribe, according to a process well known in the later Roman Empire:

There were exceptions to this practice, such as:

Some of these would disappear later, replaced by Normanic names; thus Coriovallum became Cherbourg and Caracotinum became Harfleur. Such changes indicate that the older inhabitants who used the earlier name were displaced by newcomers, either leaving completely or becoming a small minority.

Some cities' Pre-Normanic names are not known, such as Honfleur or Dieppe.

The most common suffix in northern France is (written -acum, -acus or -aco in early Medieval Latin documents, but pronounced in vulgar Latin -acu), that means "place of" or "property". Its origin is the Celtic -āko(n). Originally, it was used to as the location of either a god or a people. Examples include Anualonacu, meaning "sanctuary of Anualō [a god]" and nautae Parisiaci, meaning "sailors of the Parisii [tribe]".

In northern France and Belgium, –(i)acum became -ay, -ai, -ey, -é or -y. All of these variations are found in Normandy. Places with this suffix include , , , and Andilly.

...
Wikipedia