What does disease mean?
Disease is a noun denoting any disorder of structure or function in a living organism that impairs health and typically produces recognizable symptoms — from infections such as influenza to chronic conditions like diabetes. It can affect humans, animals, and plants, and it is distinguished from injury, which arises from external physical harm. Beyond medicine, disease is used figuratively to describe corruption or dysfunction within organizations, economies, or societies, as in "a disease of complacency." In register, the word is neutral and standard across both formal and everyday contexts, though it sounds more clinical than "illness," which emphasizes the sufferer's experience. Its collocations are numerous: heart disease, chronic disease, infectious disease, and the prevention or spread of disease all appear frequently in news, science writing, and public-health discourse. Understanding "disease" is essential for following medical reporting, scientific literature, and discussions of global health.
A disorder of structure or function in a human, animal, or plant that impairs normal functioning and is typically manifested by distinguishing signs and symptoms.
"Doctors worked for years to identify the rare genetic disease affecting the family."
Often modified by another noun naming the type or location: heart disease, skin disease, liver disease.
A harmful or corrupting condition within a system, organization, or society.
"Bureaucratic inertia has become a disease eating away at the agency's effectiveness."
Used when referring to multiple distinct conditions or to the category as a whole, as in medical literature and public-health writing.
"Advances in genomics have transformed how researchers classify diseases."
The word "disease" literally means "not at ease" — every illness is, etymologically speaking, simply the absence of ease.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of disease
Disease entered English in the late Middle Ages as a compound of the Old French prefix "des-" (from Latin "dis-", indicating negation or reversal) and "aise", meaning ease or comfort — so its original sense was simply "lack of ease." Over time it narrowed from general discomfort to specifically mean a bodily ailment, displacing older words like "sickness" in many contexts. It shares this root with related words built on "ease", including "easy", "uneasy", and "diseased".
Related word forms
How disease is actually used
In medical contexts, "disease" is precise and clinical; "illness" is often preferred for the patient's experience. The plural "diseases" is common when discussing categories or outbreaks. In figurative use (e.g., "a disease of the mind," "a disease in society") the word carries strongly negative connotation.
Easily confused with disease
"Dis-ease" (usually written with a hyphen) is a modern term meaning a state of unease or lack of comfort, whereas "disease" refers to a medical disorder.
"Illness" typically refers to a person's subjective experience of being unwell, while "disease" names an objectively identifiable pathological condition — one can have a disease without feeling ill, and feel ill without having a diagnosable disease.