Gallo-Brittonic languages
The Gallo-Brittonic languages, also known as the P-Celtic languages, are a proposed subdivision of the Celtic languages containing the languages of Ancient Gaul (both Celtica and Belgica) and Celtic Britain, which share certain features. Besides common linguistic innovations, speakers of these languages shared cultural features and history.
Source: Wikipedia — Gallo-Brittonic languages (CC BY-SA 4.0)