The Collaborative International Dictionary of English v.0.48:

Molasses \Mo*las"ses\, n. [F. m['e]lasse, cf. Sp. melaza, Pg.
   mela[,c]o, fr. L. mellaceus honeylike, honey-sweet, mel,
   mellis, honey. See Mellifluous, and cf. Melasses.]
   The thick, brown or dark colored, viscid, uncrystallizable
   sirup which drains from sugar, in the process of manufacture;
   any thick, viscid, sweet sirup made from vegetable juice or
   sap, as of the sorghum or maple. See Treacle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

molasses
    n 1: thick dark syrup produced by boiling down juice from sugar
         cane; especially during sugar refining