1. A gradual decline in quality, serviceability, or vigor: Ted's mother noticed a gradual deterioration and change in the health of her friend Jim because of his illness and prolonged stay in the hospital.
2. The process of becoming worse: Mike's aunt stated that she was very concerned that the quality of service at the hotel was suffering a deterioration and changing for the worse.

There has been a steady deterioration of academic standards in Monroe's local college.

3. A downturn, a decline, or a significant downward trend: The economic deteriorations are having detrimental influences on more and more people.
4. In psychiatry, progressive impairment in mental functioning without the implication of irreversibility: Due to Shirley's chronic alcoholism, the doctors indicated that her mental deterioration was permanent and there was no hope of recovery.
5. Depreciation or loss of value of real property due to physical wear and tear: The value of the riverside property suffered significant deterioration as a result of the recurring flood pattern of the river.
6. Etymology: from Late Latin deterioratus, the past participle of deteriorare, "to make worse, to become worse" which came from Latin deterior, "lower, inferior, worse".

Dementia occurring with people who are chronically addicted to alcohol: Al's doctor explained that his condition was called alcoholic deterioration which had resulted in a severe decline of his normal mental abilities.

Dementia that is caused by alcoholic deterioration is an organic mental disorder characterized by a general loss of intellectual abilities involving the impairment of memory, judgment, and abstract thinking, as well as changes in personality.

Impairment of the ability to maintain one's level of concentration despite an apparent desire to do so and a lack of competing thoughts that explain ordinary inattentiveness: The patient in the nursing home appeared to be suffering from a deterioration of attention which was revealed when she would struggle to concentrate and was unable to do it.

The clinical picture in which a psychotic patient becomes apathetic and shows a loss of interest in his or her appearance, environment, and social adjustments: The emotional deterioration of the patient’s condition was dramatic as she showed no interest in nor cared how she looked.

A slowly progressing decline in physical and mental health, apparently as a result of natural causes resulting from the processes of aging: Karen was worried about the senile deterioration of her neighbor who was almost 90 years old and was no longer able to go for walks without hanging on to her daughter's arm.

Mike's neighbor, who was 85 and formerly an Olympic swimmer, apologized because he figured that his senile deterioration was limiting him to swim 29 laps; while his younger neighbor, who is 55 years old, thought he was doing pretty good when he could swim nine laps.