depression

Depression is a state of sadness, a low place on a surface or an extended period of economic recession. (noun)

An example of depression is when you feel sad all the time.
An example of depression is the indentation made by a thumb in a piece of soft clay.
An example of depression is when an economic recession has gone on for a long time.

See depression in Webster's New World College Dictionary

noun

a depressing or being depressed
a depressed part or place; hollow or low place on a surface
low spirits; gloominess; dejection; sadness
a decrease in force, activity, amount, etc.
Astron. the angular distance of a celestial body below the horizon
☆ Econ. a period marked by slackening of business activity, widespread unemployment, falling prices and wages, etc.
Med. a decrease in functional activity
Meteorol.
1. a lowering of the atmospheric pressure indicated by the fall of mercury in a barometer
2. an area of relatively low barometric pressure; low
Psychol. an emotional condition, either neurotic or psychotic, characterized by feelings of hopelessness, inadequacy, etc.
Surveying the angular distance of an object below the horizontal plane

See depression in American Heritage Dictionary 4

(dĭ-prĕshˈən)

noun

a. The act of depressing.
b. The condition of being depressed.
An area that is sunk below its surroundings; a hollow.
The condition of feeling sad or despondent.
Psychology A psychiatric disorder characterized by an inability to concentrate, insomnia, loss of appetite, anhedonia, feelings of extreme sadness, guilt, helplessness and hopelessness, and thoughts of death. Also called clinical depression.
a. A reduction in activity or force.
b. A reduction in physiological vigor or activity: a depression in respiration.
c. A lowering in amount, degree, or position.
Economics
a. A period of drastic decline in a national or international economy, characterized by decreasing business activity, falling prices, and unemployment.
b. Depression The worldwide economic depression from the late 1920s through the 1930s. In the United States, it began with the stock market crash in October, 1929.
Meteorology A region of low barometric pressure.
The angular distance below the horizontal plane through the point of observation.
Astronomy The angular distance of a celestial body below the horizon.