An Etymological Dictionary of Astronomy and Astrophysics

1. Meteo.: Any form of water, such as rain, snow, sleet, or hail, that falls to the Earth’s surface. The quantity of such water falling in a specific area within a specific period.
   
2. Chemistry: The process of separating a solid substance from a solution.

Etymology (EN): From M.Fr. précipitation, from L. præcipitationem “act or fact of falling headlong, haste,” from præcipitare “fall, be hasty,” from præceps “steep, headlong, headfirst,” from præ- “forth” + caput, → head.

Etymology (PE): 1) Bâreš, verbal noun of bâridan “to rain,” bârân “rain;” Mid.Pers. vâritan, vârân; Av. vār- “rain; to rain;” cf. Skt. vār- “rain, water; to rain;” PIE base *uer- “water, rain, river.”
Rizeš, verbal noun of rixtan “to flow, to pour,” → overflow.

2. Tahnešast “to settle down, precipitate,” from
   tah “→ bottom, end;” + nešast past stem of nešastan “to sit down; to settle down; to sink,” → sit.