Dictionary of Family Names

CLAY.   A town of France in Seine.  A lake on the isle of Lewis, Scotland.  Clee, hills in Wales.  Cle, left-handed, a place lying to the left, in relation to another place. Cledh, cloid, and cladd, in the Gaelic, Welsh, and British, signify a ditch, a trench, a wall; cladh, a church-yard; cledd, Welsh, a sword; Gaelic, claiheamb, from which we have Claymore, a large sword.  The same word in Welsh and Gaelic that signifies a river is often applied to a sword, from their resemblance in glittering brightness.