An Etymological Dictionary of Astronomy and Astrophysics

The normal oxide of hydrogen with formula H₂O. Pure water’s → melting point is 0°C and its → boiling point 100 °C at sea level. Water has a → maximum density at very nearly 4°C of (by definition) 1.0000 g cm^-3. It then expands as its temperature drops to 0°C, the density being 0.9998 g cm^-3 . On freezing, it expands still further, giving ice a density of 0.9168 g cm^-3 at 0°C, whereas water has a density of 0.9998 g cm^-3 at 4 °C.

A → water molecule consists of one → oxygen (O) atom bonded to two → hydrogen (H) atoms.

The → specific heat of water, 1 calorie per gram per 1 degree C (cal/g/°C), is higher than most other substances. Therefore, water both absorbs and releases heat more slowly than land. This causes land areas to heat more rapidly and to higher temperatures and also cool more rapidly and to lower temperatures, compared to oceans. The high heat capacity of water also explains why the temperatures of land near a body of water are more moderate. The high heat capacity of water keeps its temperature within a relatively narrow range, causing nearby coastal areas to also have a narrow daily and seasonal temperature range. See also → heavy water, → ortho-water, → para-water.

Etymology (EN): Water, from O.E. wæter (cognates: Du. water; O.H.G. wazzar; Ger. Wasser; Goth. wato); cf. Gk. hydro-, combining form of hydor “water,” cognate with Skt. udá- “water;” Khotanese ūtcā “water;” Hittite uātar; L. unda “wave;”
O.C.S., Rus. voda; Lith. vanduo; from PIE base *wed- “water; wet.”

Etymology (PE): Âb “water,” variants iv, êw, âp; from
Mid.Pers. âb “water;” O.Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
Hitt. happa- “water;” PIE āp-, ab- “water, river;”
cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis);
O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook.”