The Collaborative International Dictionary of English v.0.48:
Malmsey \Malm"sey\, n. [OE. malvesie, F. malvoisie, It. malvasia, malavagia, fr. Malvasia, or Napoli di Malvasia, in the Morea.] A kind of sweet wine from Crete, the Canary Islands, etc. --Shak. [1913 Webster]WordNet (r) 3.0 (2006):
malmsey n 1: sweet Madeira wine