Meaning

noun tropical annual procumbent poisonous subshrub having fruit that splits into five spiny nutlets; serious pasture weed

noun a plant of the genus Trapa bearing spiny four-pronged edible nutlike fruits

noun Mediterranean annual or biennial herb having pinkish to purple flowers surrounded by spine-tipped scales; naturalized in America

originFrom Middle English calketrappe, from Old English calcatrippe, from Medieval Latin calcatrippa (“thistle”), from Latin calx or calcare (“to tread”) + trappa (“trap”).

Etymology from Wiktionary, CC BY-SA 3.0