amphipathic UK /ˌam.fɪˈpaθ.ɪk/US /ˌæm.fəˈpæ.θɪk/ adjective2 •Describing a molecule, such as a detergent, which has both hydrophobic and hydrophilic groups. •Of the surface(s) on a protein, particularly an alpha helix, where one surface of the alpha helix has hydrophilic amino acids and the opposite face has hydrophobic (or lipophilic) amino acids.