Definition:

"Disease"

An impairment of health or a condition of abnormal functioning illness, sickness, unwellness, malady - impairment of normal physiological function affecting part or all of an organism.

Another dictionary..

A pathological condition of a part, organ, or system of an organism resulting from various causes, such as infection, genetic defect, or environmental stress, and characterized by an identifiable group of signs or symptoms

Wikkipedia definition of Disease define