Cos, a priest.  Having lost some former references, of years back, relating to this term, my proofs will be somewhat impaired.  I must chiefly point out that we have coz in the Cornish dialct, as an "elder," as we find from Borlase; and koz in the Armorican, in the same sense as Villemarqué informs us.  We may consider it sufficiently ascertained from the inscription found under the church of Nôtre Dame, as in Montfaucon, vol. ii. pl. 190, and p. 424, that the Druids were called Senani, or elders: which word may be considered to be well paralleled by coz in Celtic, implying "elder," as we have seen.  In fact, we find that a priest was called presbyter, or elder, in Greek.  This word, I take it, explains a line of Celtic which has been hitherto not understood.  When Caesar was taken prisoner by a skirmishing party of the Gauls, his life was preserved, and his release was procured, by one of the enemy, who exclaimed to his captor, "Ke Cos Kaiser"; that is, "let go Caesar, the Pontifex Maximus, i.e., the Cos, or priest"; which words, as Servius, an author of the fifth century, tells us, who relates the anecdote in his Notes to Virgil, had the desired effect.  The superstitious Gaul might have supposed that he should draw down upon himself personally and individually the vengeance of all the heathen divinities worshipped by Caesar—the thirty thousand gods of Rome—if he should injure their high priest.  Like many other important Celtic words, it had a close alliance with the ancient Hebrew, as Baxter well observes in his Glossary (Preface, p. iv), of the word cohen in the latter language, which stands in juxtaposition with the very similar word in ancient British, and with precisely the same signification in both languages, of priest and senator. (Celtic Inscriptions on Gaulish & British Coins, Poste, 1861)