- an acute and highly contagious bacterial disease causing inflammation of the mucous membranes, formation of a false membrane in the throat which hinders breathing and swallowing, and potentially fatal heart and nerve damage by a bacterial toxin in the blood. It is now rare in developed countries owing to immunization.
- The disease is caused by Corynebacterium diphtheriae: see Klebs-Löffler bacillus
mid 19th century: modern Latin, from French diphthérie (earlier diphthérite), from Greek diphthera 'skin, hide'
In the past diphtheria was pronounced with an f sound representing the two letters ph (as in telephone, sulphur, and other ph words derived from Greek). In recent years the pronunciation has shifted and today the most common pronunciation, no longer incorrect in standard English, is with a p sound. A very similar shift has taken place with the word diphthong, which is now also widely pronounced with a p rather than an f sound.