cactus (n.)

c. 1600, in a classical sense, "cardoon, artichoke," from Latin cactus, from Greek kaktos, name of a type of prickly plant of Sicily (the Spanish artichoke), a "foreign word of unknown origin" [Beekes]. In reference to the green, leafless, spiked American plants from 1769, because Linnaeus gave the name to them thinking they were related to the classical plant. Related: Cactal.