a disease of the body or mind, or the condition of being illCOLLOCATIONS COLLOCATIONS have an illness/suffer from an illness recover from an illness serious illness minor illness short/long illness childhood illness acute illness (=an illness that becomes serious very quickly) chronic illness (=an illness that lasts a long time and cannot be cured) fatal illness (=an illness which causes death) terminal illness (=an illness which cannot be cured and that causes death, often slowly) mental illness the symptoms of an illness (=the things that show that someone has it) through illness (=because of illness)
ways to improve your health and reduce the risk of illness
➔diseaseWORD CHOICE: WORD CHOICE: illness, diseaseIllness and disease are often used in the same way and are equally common in spoken English. However, illness is more often used to refer to the length of time or state of being unwell• He died after a long illness. • if you are off school because of illness!! Do not use illness to talk about less serious problems such as headaches or colds.Disease is a particular kind of illness, especially one that spreads from one person to another or affects a particular part of your body• infectious diseases • heart disease!! Disease can also be used to mean a lot of different diseases• Cigarette smoking causes death and disease.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.