slump

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To fall or sink heavily; collapse.
• intransitive verb To droop, as in sitting or standing; slouch.
• intransitive verb To decline suddenly; fall off.
• intransitive verb To perform poorly or inadequately.
• intransitive verb To sink or settle, as into mud or slush.
• intransitive verb To slide down or spread out thickly, as mud or fresh concrete.
• noun The act or an instance of slumping.
• noun A drooping or slouching posture.
• noun A sudden falling off or decline, as in activity, prices, or business.
• noun An extended period of poor performance, especially in a sport or competitive activity.

from The Century Dictionary.

• To fall or sink suddenly when walking on a surface, as on ice or frozen ground, not strong enough to support one; walk with sinking feet; sink, as in snow or mud.
• Hence, to fail or fall through ignominiously: often with through; as, the plan slumped through.
• noun A gross amount; a block; lump: as, to buy or take things in the slump: also used attributively: as, a slump sum.
• noun A boggy place; soft, swampy ground; a marsh; a swamp.
• noun The noise made by anything falling into a hole or slump.
• noun The act of slumping through weak ice or any frozen surface, or into melting snow or slush.
• noun Hence, an ignominious coming to naught; complete failure; also, a sudden fall, as of prices: as, a slump in stock from 150 to 90.
• To throw or bring into a mass; regard as a mass or as a whole; lump.

from the GNU version of the Collaborative International Dictionary of English.

• noun Scot. The gross amount; the mass; the lump.
• transitive verb To lump; to throw into a mess.
• noun Prov. Eng. & Scot. A boggy place.
• noun Scot. The noise made by anything falling into a hole, or into a soft, miry place.
• noun colloq. A falling or declining, esp. suddenly and markedly; a falling off
• intransitive verb To fall or sink suddenly through or in, when walking on a surface, as on thawing snow or ice, partly frozen ground, a bog, etc., not strong enough to bear the person.
• intransitive verb To slide or slip on a declivity, so that the motion is perceptible; -- said of masses of earth or rock.
• intransitive verb colloq. To undergo a slump, or sudden decline or falling off.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive To collapse heavily or helplessly.
• verb intransitive To decline or fall off in activity or performance.
• verb intransitive To slouch or droop.
• noun A heavy or helpless collapse; a slouching or drooping posture; a period of poor activity or performance, especially an extended period.
• noun Scotland, UK, dialect A boggy place.
• noun Scotland The noise made by anything falling into a hole, or into a soft, miry place.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb assume a drooping posture or carriage
• noun a long-term economic state characterized by unemployment and low prices and low levels of trade and investment
• verb go down in value
• verb fall or sink heavily
• verb fall heavily or suddenly; decline markedly
• noun a noticeable deterioration in performance or quality