• A concomitant but unrelated disease or pathologic process; usually used in epidemiology to indicate the coexistence of two or more disease processes.
  CRISP Thesaurus
  National Institutes of Health, 2006
• The coexistence of two or more disease processes.
  NCI Thesaurus
  U.S. National Cancer Institute, 2021
• The condition of having two or more diseases at the same time.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• 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.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021
• (intercurrent illness) A disease occurring during the course of another disease with which it has no connection.
  ACC/AHA Clinical Data Terminology
  American College of Cardiology and American Heart Association , 2020