Where does “Prydeindod” come from?

Prydeindod (Welsh) comes from Welsh Prydain, from Middle Welsh Prydein, from Proto-Brythonic Pritanī, from Proto-Celtic *Kʷritanī, from Proto-Indo-European kʷer- — to do; to make; to build.

Prydeindod (Welsh): Britishness