n.1 a Psychol. a state of extreme dejection or morbidly excessive melancholy; a mood of hopelessness and feelings of inadequacy, often with physical symptoms. b a reduction in vitality, vigour, or spirits.
2 a a long period of financial and industrial decline; a slump. b (the Depression) the depression of 1929-34.
3 Meteorol. a lowering of atmospheric pressure, esp. the centre of a region of minimum pressure or the system of winds round it.
4 a sunken place or hollow on a surface.
5 a a lowering or sinking (often foll. by of : depression of freezing-point). b pressing down.
6 Astron. & Geog. the angular distance of an object below the horizon or a horizontal plane.
Etymology: ME f. OF or L depressio (as DE-, premere press- press)