porphyrin Syllabification: (por·phy·rin)Pronunciation: /ˈpôrfərin/Definition of porphyrin noun Biochemistry any of a class of pigments (including heme and chlorophyll) whose molecules contain a flat ring of four linked heterocyclic groups, sometimes with a central metal atom. Origin: early 20th century: from Greek porphura 'purple' + -in1porphyrin in other Oxford dictionaries Definition of porphyrin in the British & World English dictionary