Diphtheritic is an adjective that describes a disease caused by the bacteria Corynebacterium diphtheriae. It is characterized by inflammation and the formation of a tough, grayish membrane in the throat and other respiratory passages. There are a few synonyms that can be used to describe this condition. These include croupous, membranous, or pharyngeal diphtheria. Additionally, the term diphtheric can be used to describe an object or substance that resembles or pertains to the disease. Overall, the use of these synonyms can help to provide a more descriptive and varied vocabulary for discussions of the disease.