Merriam-Webster Collegiate Dictionary - hasid

 also Chasid or Chassid  noun  (plural ~im; also Chasidim or Chassidim)  Etymology: Hebrew ?asidh pious  Date: 1812  1. a member of a Jewish sect of the second century B.C. opposed to Hellenism and devoted to the strict observance of the ritual law  2. (also Hassid) a member of a Jewish mystical sect founded in Poland about 1750 in opposition to rationalism and ritual laxity  • ~ic also Hassidic or Chasidic or Chassidic adjective