"caltrop" in the noun sense
1. caltrop, devil's weed, Tribulus terestris
tropical annual procumbent poisonous subshrub having fruit that splits into five spiny nutlets serious pasture weed
2. water chestnut, water chestnut plant, caltrop
a plant of the genus Trapa bearing spiny four-pronged edible nutlike fruits
3. star-thistle, caltrop, Centauria calcitrapa
Mediterranean annual or biennial herb having pinkish to purple flowers surrounded by spine-tipped scales naturalized in America
Source: WordNet® (An amazing lexical database of English)
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