a. [ Gr. e'y^ well + &unr_; sulphur + &unr_; color. ] (Chem.) Pertaining to, or denoting, an acid so called. [ 1913 Webster ]

Euthiochroic acid (Chem.), a complex derivative of hydroquinone and sulphonic (thionic) acid. -- so called because it contains sulphur, and forms brilliantly colored (yellow) salts. [ 1913 Webster ]