Its source is clerec, an Old English name meaning "Priest."
During the European Middle Ages, Clark was often used as an occupational surname for scribes or secretaries in religious orders. Some of these were allowed to marry and pass on the name, unlike the monks and priests with whom they shared the then unusual distinction of being literate.
The terms ''clerk'' and ''cleric'' both evolved from this same source. This is apparent when we compare the phrase ''clerical skills,'' which refers to the skills of a secretary, with ''clerical garb,'' which refers to the dress of the clergy.