noun

• (psychology, usually uncountable) A state of mind producing serious, long-term lowering of enjoyment of life or inability to visualize a happy future.
• (psychology, countable) A period of low morale or unhappiness (a period of experiencing the above-mentioned state of mind) which lasts longer than several weeks and may include ideation of self-inflicted injury or suicide.
• (geography) An area that is lower in topography than its surroundings.
• (meteorology) An area of lowered air pressure that generally brings moist weather, sometimes promoting hurricanes and tornadoes.
• (economics) A period of major economic contraction.
• (economics, US) Four consecutive quarters of negative, real GDP growth. See NBER.
• The act of lowering or pressing something down.
• (biology, physiology) A lowering, in particular a reduction in a particular biological variable or the function of an organ, in contrast to elevation.
• Synonym of Great Depression.