co·balt (k??bôlt?)n. Symbol Co A hard, brittle metallic element, found associated with nickel, silver, lead, copper, and iron ores and resembling nickel and iron in appearance. It is used chiefly for magnetic alloys, high-temperature alloys, and in the form of its salts for blue glass and ceramic pigments. Atomic number 27; atomic weight 58.9332; melting point 1,495°C; boiling point 2,927°C; specific gravity 8.9; valence 2, 3. See Periodic Table.[German Kobalt, from Middle High German kobolt, variant of kobold, goblin (from silver miners’ belief that cobalt had been placed by goblins who had stolen the silver); see kobold.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.cobalt (?k??b??lt) n (Elements & Compounds) a brittle hard silvery-white element that is a ferromagnetic metal: occurs principally in cobaltite and smaltite and is widely used in alloys. The radioisotope cobalt-60, with a half-life of 5.3 years, is used in radiotherapy and as a tracer. Symbol: Co; atomic no: 27; atomic wt: 58.93320; valency: 2 or 3; relative density: 8.9; melting pt: 1495°C; boiling pt: 2928°C[C17: German Kobalt, from Middle High German kobolt goblin; from the miners’ belief that malicious goblins placed it in the silver ore]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014co?balt (?ko? b?lt) n. a hard, ductile element occurring in compounds whose silicates afford important blue coloring substances for ceramics. Symbol: Co; at. wt.: 58.933; at. no.: 27; sp. gr.: 8.9 at 20°C. [1675?85;