an·ti·diph·the·rit·ic I. \| ̷ ̷(ˌ) ̷ ̷ˌ ̷ ̷ ̷ ̷|-\adjective Etymology: International Scientific Vocabulary anti- (I) + diphtheritic : preventing diphtheria especially by immunization < immunization with antidiphtheritic toxoid > II. noun (-s) : an agent that prevents or modifies the course of diphtheria < antitoxin is an antidiphtheritic >