Author: Adam Moore (LÆMEUR) <email@example.com>
Date: December 27, 2012
All Those Painted Men of The North
You wouldn't know by looking, but the words Cruithne and Prydain are, in fact, cognates.
It seems that humans sometimes have a tendency to migrate the leading labio-velar consonants of their languages into unvoiced bilabial consonants — in other words, the K^w sound at the beginning of quark becomes a P sound, as in park. At some point prior to the medieval era, this happened in the insular Celtic languages. The Celts of what is now Ireland retained the leading K^w sound in their words, while the Celts of what is now Wales transformed it into a P sound; linguists call these two branches of the same root language Q Celtic and P Celtic, respectively.
The modern word Britain comes from a P Celtic antecedent of the modern Welsh word, Prydain (pronounced PRIH-dine). Cruithne (pronounced somewhat like CROON-ya) is a modern Irish word derived from Prydain's Q Celtic equivalent.
Both of these words, and their parent word, are understood to mean something akin to "people of forms" — the Gaelic root, cruth, and the Welsh root, pryd, coming from the reconstructed proto-Celtic k^writu-, "shape, appearance" — and this is understood to mean people who tattooed or war-painted or otherwise decorated their bodies.