1) Acid used in dyeing 2) Stinky sort of acid 
• (a.) Pertaining to, or designating, an acid of the ethylene series, metameric with fumaric acid and obtained by heating malic acid.
Ma·le'ic adjective [ Confer French maléique . See Malic .] (Chemistry) Pertaining to, or designating, an acid of the ethylene series, metameric with fumaric acid and obtained by heating malic acid.