"breed of heavy draught horses," 1786, so called because they were bred in the valley of the Clyde in Scotland. The river name is perhaps literally "cleansing," from a Celtic root akin to Latin cloaca (see cloaca).
Entries linking to clydesdale
cloaca n.
1650s, euphemism for "underground sewer," from Latin cloaca "public sewer, drain," from cluere "to cleanse," probably from PIE root *kleu- "to wash, clean" (source also of Greek klyzein "to dash over, wash off, rinse out," klysma "liquid used in a washing;" Lithuanian šluoju,šluoti "to sweep;" Old English hlutor, Gothic hlutrs, Old High German hlutar, German lauter "pure, clear"). Use in biology, in reference to eliminatory systems of lower animals, is from 1834. Related: Cloacal (1650s); cloacinal (1857).
Clyde
masc. proper name, from the family name, from the region of the Clyde River in Scotland (see Clydesdale). Most popular in U.S. for boys c. 1890-1910, falling off rapidly thereafter, hence probably its use in 1940s teenager slang for "a square, one not versed in popular music or culture."