Note 39 — Chapter IX · Place-name Stories
Reading edition
In some native Welsh words we have an option between a prefix ym and am, an option arising out of the fact that originally it was neither ym nor am, but m̥, for an earlier m̥bi, of the same origin as Latin ambi and Greek ἀμφί, ‘around, about.’ The article, its meaning in the combination in banbh being forgotten, would fall under the influence of the analogy of the prefix, now am or ym, so far as the pronunciation was concerned. ↑