bilin|ˈbaɪlɪn| [f. bile + -in.] A gummy pale yellow mass, formerly considered to be the principal constituent of the bile. 1849–52Todd Cycl.Anat. & Phys. IV. 844/2 Bilin and biliary colouring matter.1872Huxley Phys. v. 122 Bilin..is a mixture of two acids in combination with soda.