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Comprehensive
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activate in chemistry, to make more reactive, as by heating. [1/6 definitions]
alkali metal any of a group of highly reactive chemical elements, such as sodium and potassium, that are typically univalent cations forming various compounds, but that can be isolated as soft, low-density metals.
alkaline-earth metal any of a group of highly reactive chemical elements, such as calcium and magnesium, that are typically divalent cations and form compounds with various other elements.
atomic clock an extremely accurate timekeeping device regulated by the reliably constant frequency at which atoms of certain highly reactive substances absorb or emit electromagnetic radiation.
cerium a highly reactive chemical element of the rare-earth group that has fifty-eight protons in each nucleus and that occurs naturally only in compounds. (symbol: Ce)
cesium a highly reactive chemical element of the alkali metal group that has fifty-five protons in each nucleus and that occurs in pure form as a soft, silvery metal melting to a heavy liquid just above room temperature. (symbol: Cs) [1/2 definitions]
europium a highly reactive chemical element of the rare-earth group that has sixty-three protons in each nucleus. (symbol: Eu)
fluorine an extremely reactive chemical element of the halogen group that has nine protons in each nucleus and that occurs naturally only in compounds such as fluoride salts, but that can be isolated in pure form as a yellowish, highly toxic gas. (symbol: F)
hyperreactive combined form of reactive.
impulse a physical force that causes reactive motion. [1/5 definitions]
iodine a highly reactive chemical element of the halogen group that has fifty-three protons in each nucleus and occurs naturally in compounds such as salts, and in pure form as a poisonous bluish black crystal. (symbol: I) [1/2 definitions]
ketone a highly reactive organic chemical compound containing a carbonyl group linked to two hydrocarbon radicals.
lanthanum a chemical element of the rare-earth group that has fifty-seven protons in each nucleus and that occurs as a soft, highly reactive, solid metal or as a trivalent ion. (symbol: La)
lithium an extremely reactive chemical element of the alkali metal group that has three protons in each nucleus, occurs naturally only in compounds such as salts, and can be isolated in pure form as a light soft solid. (symbol: Li) [1/2 definitions]
magnesium a highly reactive chemical element of the alkaline-earth group that has twelve protons in each nucleus and that occurs naturally only in compounds, but that can be isolated as a divalent ion essential in plant and animal nutrition, or as alight, ductile, silver-white solid that bursts into a bright flame when heated above room temperature, used for flares, fireworks, and the like. (symbol: Mg)
nonreactive combined form of reactive.
reflex reactive or responsive. [1/7 definitions]
rubidium a highly reactive chemical element of the alkali metal group that has thirty-seven protons in each nucleus, that occurs naturally only in compounds with oxygen and other elements, but that can be isolated as a liquid or very soft solid metal. (symbol: Rb)
sodium a highly reactive chemical element of the alkali metal group that has eleven protons in each nucleus and that occurs naturally only in compounds such as sodium chloride and sodium bicarbonate. (symbol: Na)
strontium a highly reactive chemical element of the alkaline-earth group that has thirty-eight protons in each nucleus, that occurs naturally only in compounds, and that has highly toxic radioactive isotopes that are by-products of some types of nuclear fission reactions. (symbol: Sr)