1.NounAny of a group of quinoid derivatives of a phenylhydrazine (typically (3E)-3-[[4-[4-[(2E)-2-(3-carboxy-4-oxocyclohexa-2,5-dien-1-ylidene)hydrazinyl]phenyl]phenyl]hydrazinylidene]-6-oxocyclohexa-1,4-diene-1-carboxylic acid); any yellow azo dye derived from such a compound