What is the X in X-mas?
masc. proper name, from Old Irish Patraicc (Irish Padraig), from Latin Patricius, literally "a patrician" (see patrician). As a given name, chiefly in northern England and Scotland, in Ireland only a popular name after 1600, due probably to the Scots settlers in Ulster. [Reaney]
Note: Many legends have grown up about Patrick: that he drove snakes out of Ireland, for example, and that he used a three-leafed clover, the shamrock, to illustrate the Trinity.