Morbiferous is an uncommon word used to describe something that is capable of causing disease or morbidity. Some synonyms for morbiferous are pathogenic, contagious, infectious, disease-carrying, unhealthy, and virulent. A pathogenic organism can cause disease in its host, while a contagious disease can be easily spread from person to person. Infectious and disease-carrying also suggest a similar capability to spread infection. Unhealthy implies that a substance or environment may be harmful to a person's well-being, and virulent means highly infectious and capable of causing severe illness. Although rarely used, the word "morbiferous" is useful when describing vectors or microbes with the potential to cause illness.