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ester

(Encyclopedia)CE5 Esters ester, any one of a group of organic compounds with general formula RCO2R′ (where R and R′ are alkyl groups or aryl groups) that are formed by the reaction between an alcohol and an...

fertilization

(Encyclopedia)CE5 Fertilization of an egg cell fertilization, in biology, process in the reproduction of both plants and animals, involving the union of two unlike sex cells (gametes), the sperm and the ovum, f...

sextant

(Encyclopedia)CE5 Sextant sextant, instrument for measuring the altitude of the sun or another celestial body; such measurements can then be used to determine the observer's geographical position or for other n...

phase, in astronomy

(Encyclopedia)CE5 Phases of the moon phase, in astronomy, the measure of how much of the illuminated surface of a planet or satellite can be seen from a point at a distance from that body; the term is most ofte...

triumphal arch

(Encyclopedia)CE5 Triumphal arch triumphal arch, monumental structure embodying one or more arched passages, frequently built to span a road and designed to honor a king or general or to commemorate a military ...

tryptophan

(Encyclopedia)CE5 tryptophan trĭpˈtəfăn [key], organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. It is one of several essent...

radio frequency

(Encyclopedia)radio frequency, range of electromagnetic waves with a frequency or wavelength suitable for communication uses. Some of these waves serve as carriers of the lower-frequency audio waves; others are mod...

valerian, in botany

(Encyclopedia)CE5 Valerian, Valeriana officinalis valerian, common name for some members of the Valerianaceae, a family chiefly of herbs and shrubs of temperate and colder regions of the Northern Hemisphere; a ...

vein

(Encyclopedia)CE5 Cross section of vein showing valves vein, blood vessel that returns blood to the heart. Except for the pulmonary vein, which carries oxygenated blood from the lungs to the heart, veins carry ...

witch hazel

(Encyclopedia)CE5 Witch hazel, Hamamelis virginiana witch hazel, common name for some members of the Hamamelidaceae, a family of trees and shrubs found mostly in Asia. The family includes the large genus (Coryl...