One-minute lesson: The name shamrock derives from the Irish word "seamrog," and means young clover. Nothing too out-there or mysterious about that. "But there's also a spiritual and religious aspect as well," Eamonn McGrath, executive director of the Irish Cultural Centre of New England, in Canton, Mass., told the Daily News. Lore holds that St. Patrick used the shamrock's three leaves to represent the Holy Trinity — you know, the Father, the Son and the Holy Ghost. A fourth leaf would have been, well, like a fifth wheel.