In a medical context, the word mortality refers to relative frequency of deaths in a specific population or location (sometimes called the mortality rate), while the word morbidity refers to the incidence or prevalence of a disease in a specific population or location (sometimes called the morbidity rate).

The related word cormorbidity is used in medical contexts to refer to the state of having multiple medical conditions at the same time.

In this context, morbidity relates to sickness, while mortality relates to death.

Both morbidity and mortality are also used in nontechnical ways. Morbidity is the noun form of the adjective morbid, which most commonly means excessively gloomy or having an unusual interest in dark subjects, like death. Morbidity, then, can be used to refer to the quality of having this interest, as in Her latest novel lacks the morbidity of her earlier works. 

Mortality, on the other hand, most commonly refers to the state or condition of being subject to death, as in Humans are aware of their own mortality. The opposite of this is immortality—unending life.

Here’s an example of mortality and morbidity used correctly in the same sentence.

Example: Studies show that while the morbidity in the region remains quite high, the mortality rate from the disease has continued to drop. 

Want to learn more? Read the full breakdown of the difference between mortality and morbidity.

Should mortality or morbidity be used in the following sentence?

It is hoped that the vaccination program will decrease _____ among the population, and, as a result, reduce the number of deaths from the disease.