Definitions for comorbidity
The presence of one or more disorders (or diseases) in addition to a primary disease or disorder.
The effect of such additional disorders or diseases.
U.S. National Library of Medicine
The presence of co-existing or additional diseases with reference to an initial diagnosis or with reference to the index condition that is the subject of study. Comorbidity may affect the ability of affected individuals to function and also their survival; it may be used as a prognostic indicator for length of hospital stay, cost factors, and outcome or survival.