"shamrocks" in the noun sense
1. white clover, dutch clover, shamrock, Trifolium repens
creeping European clover having white to pink flowers and bright green leaves naturalized in United States widely grown for forage
2. common wood sorrel, cuckoo bread, shamrock, Oxalis acetosella
Eurasian plant with heart-shaped trifoliate leaves and white purple-veined flowers
3. hop clover, shamrock, lesser yellow trefoil, Trifolium dubium
clover native to Ireland with yellowish flowers often considered the true or original shamrock
Source: WordNet® (An amazing lexical database of English)
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