noun

illness

A disease or the state of being unwell.

Her illness keeps her home from work for several days.

Etymology

The state-noun ending turns ill into the condition of being unwell. The noun can identify either that general condition or a particular disease causing it.

More examples

  • He is recovering from a serious illness.
  • Frequent handwashing helps prevent the spread of common illnesses.
  • The clinic treats both physical and mental illness.

Forms

illness · illnesses

ill adjective — Suffering from disease or poor health.

Similar words

disease
Names a specific medical condition, rather than unwellness generally.
sickness
Often interchangeable, but can specifically refer to nausea.
ailment
Usually describes a minor or less serious health problem.