in Britain, "lettuce-like salad plant of the daisy family;" in U.S., "blanched shoots of Cichorium intybus" (a plant related to the Cichorium endiva, the British "endive"), late 14c., from Old French endive (14c.), from Medieval Latin endivia or a related Romanic source, from Latin intibus. This probably is connected in some way with Medieval Greek entybon, which Klein says is perhaps of Eastern origin (compare Egyptian tybi "January," the time the plant grows in Egypt). Century Dictionary says Arabic hindiba is "appar. of European origin."
Few culinary terms cause such confusion as endive and chicory. The basic problem is that what the British call endive the Americans call chicory, and what the British call chicory the Americans call endive (the French side with the Americans: British endive translates as French chicorée). [Ayto, "Diner's Dictionary"]
The original sense of the word in Middle English was the same as the modern American one, but when the Cichorium endiva, distinguished by its annual root, much longer unequal pappus, and less bitter taste, arrived in Europe from Asia in the 16c., the confusion of names began.