precipitation

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

• noun Any form of water, such as rain, snow, sleet, or hail, that falls to the earth's surface.
• noun The quantity of such water falling in a specific area within a specific period.
• noun A hastening or acceleration, especially one that is sudden or unexpected.
• noun Abrupt or impulsive haste.
• noun A headlong fall or rush.
• noun Chemistry The process of separating a substance from a solution as a solid.

from The Century Dictionary.

• noun The act of casting down from a height, or the state of being flung or hurled downward.
• noun Rapid motion; a hurrying or rushing onward.
• noun Haste; hurry; unwise or rash rapidity.
• noun In chem., the process by which any substance is made to separate from another or others in solution, and fall to the bottom.
• noun Moisture from the atmosphere deposited on the earth's surface, including dew, mist, rain, frost, snow, sleet, hail, etc.

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

• noun The act of precipitating, or the state of being precipitated, or thrown headlong.
• noun A falling, flowing, or rushing downward with violence and rapidity.
• noun Great hurry; rash, tumultuous haste; impetuosity.
• noun (Chem.) The act or process of precipitating from a solution.
• noun (Meteorology) A deposit on the earth of hail, mist, rain, sleet, or snow; also, the quantity of water deposited.

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

• noun meteorology Any or all of the forms of water particles, whether liquid or solid, that fall from the atmosphere (e.g., rain, hail, snow or sleet). It is a major class of hydrometeor, but it is distinguished from cloud, fog, dew, rime, frost, etc., in that it must fall. It is distinguished from cloud and virga in that it must reach the ground.
• noun A hurried headlong fall.
• noun countable, chemistry A reaction that leads to the formation of a heavier solid in a lighter liquid; the precipitate so formed at the bottom of the container.
• noun figuratively Unwise or rash rapidity; sudden haste.

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

• noun the quantity of water falling to earth at a specific place within a specified period of time
• noun the falling to earth of any form of water (rain or snow or hail or sleet or mist)
• noun the process of forming a chemical precipitate
• noun the act of casting down or falling headlong from a height
• noun an unexpected acceleration or hastening
• noun overly eager speed (and possible carelessness)