illness Meaning, Definition & Usage

  1. noun impairment of normal physiological function affecting part or all of an organism
    malady; unwellness; sickness.

WordNet

Ill"ness noun
Etymology
From Ill.
Definitions
  1. The condition of being ill, evil, or bad; badness; unfavorableness. Obs. "The illness of the weather." Locke.
  2. Disease; indisposition; malady; disorder of health; sickness; as, a short or a severe illness.
  3. Wrong moral conduct; wickedness. Shak. Syn. -- Malady; disease; indisposition; ailment. -- Illness, Sickness. Within the present century, there has been a tendency in England to use illness in the sense of a continuous disease, disorder of health, or sickness, and to confine sickness more especially to a sense of nausea, or "sickness of the stomach."

Webster 1913