kohlrabi n.

"cabbage," a dialectal survival of Middle English col, from late Old English cawel, or perhaps from or influenced by cognate Old Norse kal. Both words are from Latin caulis "stem, stalk" (which in Vulgar Latin replaced brassica as the usual word for "cabbage"), from Proto-Italic *kauli- "stalk," from PIE root *(s)kehuli- "stem of a plant, stalk" (source also of Old Irish cual "faggot, bundle of sticks," Greek kaulos "stem, stalk, pole," Armenian c'awl "stalk, straw," Old Prussian kaulan, Lithuanian káulas "bone").

Latin caulis "cabbage" is the source also of Italian cavolo, Spanish col, Old French chol, French chou; it also was borrowed elsewhere in Germanic, for example Swedish kål, Danish kaal, German Kohl, Dutch kool.

kind of cruciferous plant (Brassica napus), late 14c., from Old French rape and directly from Latin rapa, rapum "turnip," which is cognate with Greek hrapys "rape," Old Church Slavonic repa, Lithuanian ropė, Middle Dutch roeve, Old High German ruoba, German Rübe "rape, turnip," perhaps a common borrowing from a non-IE word (de Vaan).

Widely grown as fodder for cattle and sheep, an oil made from it is used in cooking (see canola). Rape-oil is attested by 1540s; rapeseed by 1570s.

There has been much confusion between rape and coleseed, either plant being known under both names; the former is sometimes called winter rape and the latter summer rape. The older writers usually distinguish the turnip and rape by the adjectives round and long(-rooted) respectively. [OED]