Where does “Pentraeth” come from?

Pentraeth (Welsh) comes from Welsh pen, from Proto-Brythonic penn, from Proto-Celtic kʷennom — head.

Ancestry of “Pentraeth”, step by step

Pentraeth traces back through two separate lines of ancestry.

via Welsh pen

StepLanguageWordMeaning
1Welshpenhead; chief; top, apex
2Proto-Brythonicpennhead
3Proto-Celtickʷennomhead

via Welsh traeth

StepLanguageWordMeaning
1Welshtraethbeach, coast
Every word from Proto-Celtic kʷennom →Every word from Proto-Brythonic penn →Every word from Welsh pen →