We don't have synonyms for melasses yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are molasses, masses and measles.
(n) :
Archaic form of molasses. [A thick, sweet syrup drained from sugarcane, especially (Canada, US) the still thicker and sweeter syrup produced by boiling down raw molasses.]
(n) :
Archaic form of molasses. [A thick, sweet syrup drained from sugarcane, especially (Canada, US) the still thicker and sweeter syrup produced by boiling down raw molasses.]