sham·rock 
(shămrŏk′)
(shămrŏk′)n.
1. A plant having compound leaves with three small leaflets, especially a clover or wood sorrel.
2. The compound leaf of one of these plants.
3. A representation of one of these plants or leaves, used as a national emblem of Ireland.
[Irish Gaelic seamróg, diminutive of seamar, clover, from Middle Irish semar; probably akin to Old Norse smári, clover, and of non-Indo-European substrate origin.]