cephalinPronunciation: /ˈsɛf(ə)lɪn, ˈkɛf-/Definition of cephalin noun [mass noun] Biochemistry any of a group of phospholipids present in cell membranes, especially in the brain. Origin: late 19th century: from Greek kephalē 'brain' + -in1cephalin in other Oxford dictionaries Definition of cephalin in the US English dictionary