Proper noun
Old Welsh
The Welsh language as it existed from about 800 until the early twelfth century (when it developed into Middle Welsh), not readily intelligible to modern Welsh speakers.
Ann Arbor, Mich: Univ. M/films The manuscript was widely thought to be in Old Welsh until the 1700s when it was identified as Cornish. Source: Internet
Most Celticists consider Geoffrey's Caliburnus to be derivative of a lost Old Welsh text in which bwlch had not yet been lenited to fwlch. Source: Internet