malmsey n.

type of strong, sweet white wine, c. 1400, from Provençal malmesie or Middle Dutch malemesye, both from Medieval Latin malmasia, from Medieval Greek Monembasia "Monemvasia," a town in the southern Peloponnesus that was an important center of wine production in the Middle Ages. The town is joined to the mainland by a causeway, and its name is literally "(town of the) one entrance," from monos "alone, only" (from PIE root *men- (4) "small, isolated") + embasis "entering into," from en- "in" + basis "a going, a stepping, a base" (see basis).

vpon that hyll is a cyte called Mal[v]asia, where first grewe Malmasye and yet dothe; howbeit hit groweth nowe more plentuously in Cadia and Modona, and no where ellys. [Sir Richard Guylforde, "Pylgrymage," 1506] 

The wine later was made in the Azores, Madeira, and the Canary Islands, but the name remained. Another form of it in Middle English was malvesy, from Old French malvesie, from Italian malvasia, the Italian form of the Greek town name.