any of certain clovers or cloverlike plants with leaflets in groups of three, used as the emblem of Ireland, as the red clover, white clover, wood sorrel, or black medic
Origin:
Ir seamrog, dim. of seamar, clover
See shamrock in American Heritage Dictionary 4
noun
Any of several plants, such as a clover or wood sorrel, having compound leaves with three small leaflets, considered the national emblem of Ireland.