morpholinePronunciation: /ˈmɔːfəliːn/Definition of morpholine noun [mass noun] Chemistry a synthetic compound used as a solvent for resins and dyes and (in the form of salts) as an ingredient of emulsifying soaps used in floor polishes. A cyclic amine; chemical formula: C4H9NO Origin: late 19th century: from morphine, with the insertion of the syllable -ol- (see -ol)morpholine in other Oxford dictionaries Definition of morpholine in the US English dictionary