pyridoxal Syllabification: (pyr·i·dox·al)Pronunciation: /ˌpiriˈdäksəl/Definition of pyridoxal noun Biochemistry an oxidized derivative of pyridoxine that acts as a coenzyme in transamination and other processes. Origin: 1940s: from pyridoxine + -alpyridoxal in other Oxford dictionaries Definition of pyridoxal in the British & World English dictionary