Zennor is a very interesting place etymologically speaking. It's believed to originate from "St. Senara", with the town's website stating "[the name originated from...] the Breton princess Azenor who was falsely accused by her husband, and thrown into the sea in a barrel and floated to Ireland, founding Zennor along the way".
What's peculiar though is that Zennor has long been recognised as a haven for the Cornish language. Whilst its name in Cornish (Eglossenar) raises few eyebrows, its commonly accepted Anglicised name (Zennor), contains a letter that does not feature in the Cornish language (the letter Z!), raising questions about etymological authenticity and anglicised place names.
A similar oddity can be observed with the suburb of Van, Caerphilly, which contains a letter V - a letter that doesn't exist in Welsh. (The suburb's Welsh Name, Y Fan, again checks out, as a singular F in Welsh is pronounced as we would a V in English)