1. [n]  overly eager speed (and possible carelessness); "he soon regretted his haste"
2. [n]  an unexpected acceleration or hastening; "he is responsible for the precipitation of his own demise"
3. [n]  the act of casting down or falling headlong from a height
4. [n]  the falling to earth of any form of water (rain or snow or hail or sleet or mist)
5. [n]  the process of forming a chemical precipitate
6. [n]  the quantity of water falling to earth at a specific place within a specified period of time; "the storm brought several inches of precipitation"

Precipitation
Provides an introduction to the different types of precipitation and explains how precipitation is related to weather.

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1. \Pre*cip`i*ta"tion\, n. (Meteor.)
   A deposit on the earth of hail, mist, rain, sleet, or snow;
   also, the quantity of water deposited.
   Note: Deposits of dew, fog, and frost are not regarded by the
         United States Weather Bureau as precipitation. Sleet
         and snow are melted, and the record of precipitation
         shows the depth of the horizontal layers of water in
         hundredths of an inch or in millimeters.
   

2. \Pre*cip`i*ta"tion\, n. [L. praecipitatio: cf. F.
   pr['e]cipitation.]
   1. The act of precipitating, or the state of being
      precipitated, or thrown headlong.
            In peril of precipitation From off rock Tarpeian.
                                                  --Shak.
   2. A falling, flowing, or rushing downward with violence and
      rapidity.
            The hurry, precipitation, and rapid motion of the
            water, returning . . . towards the sea. --Woodward.
   3. Great hurry; rash, tumultuous haste; impetuosity. ``The
      precipitation of inexperience.'' --Rambler.
   4. (Chem.) The act or process of precipitating from a
      solution.
   

1. 1. The process of a solid settling out of a solution, or the sum of the settled particles.
   2. Rain, snow, hail, etc.
   3. In immunology, a reaction between a soluble antibody and a solid antigen, which forms a material that precipitates out of the antibody-antigen solution.
2. Discharge of atmospheric moisture as rain, snow or hail, measured in depth of fall or in terms of intensity of fall in unit time.