[plat-n-uhm, plat-nuhm]
Chemistry. a heavy, grayish-white, highly malleable and ductile metallic element, resistant to most chemicals, practically unoxidizable except in the presence of bases, and fusible only at extremely high temperatures: used for making chemical and scientific apparatus, as a catalyst in the oxidation of ammonia to nitric acid, and in jewelry. Symbol: Pt; atomic weight: 195.09; atomic number: 78; specific gravity: 21.5 at 20°C.
a light, metallic gray with very slight bluish tinge when compared with silver.
made of platinum.
(of a record, CD, or cassette) having sold a minimum of one million copies.

1805–15; < Neo-Latin, alteration of earlier platina < Spanish; see platina Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
platinum (ˈplætɪnəm)
1.  a ductile malleable silvery-white metallic element, very resistant to heat and chemicals. It occurs free and in association with other platinum metals, esp in osmiridium: used in jewellery, laboratory apparatus, electrical contacts, dentistry, electroplating, and as a catalyst. Symbol: Pt; atomic no: 78; atomic wt: 195.08; valency: 1--4; relative density: 21.45; melting pt: 1769°C; boiling pt: 3827±100°C
2.  a.  a medium to light grey colour
 b.  (as adjective): a platinum carpet
[C19: New Latin, from platina, on the model of other metals with the suffix -um]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1812, from Mod.L., from Sp. platina "platinum," dim. of plata "silver," from O.Fr. plate or O.Prov. plata "sheet of metal" (see plate). The element so called because it looks like silver. Earlier taken directly from Sp. as platina (c.1750). As a shade of blond hair, attested
from 1931. As a designation for a recording that has sold at least one million copies, it is attested from 1971.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

platinum plat·i·num (plāt'n-əm)
Symbol Pt
A ductile malleable metallic element usually occurring mixed with other metals such as iridium, osmium, or nickel and used as a catalyst and in dentistry. Atomic number 78; atomic weight 195.08; melting point 1,768°C; boiling point 3,825°C; specific gravity 21.45; valence 2, 3, 4.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
platinum   (plāt'n-əm)  Pronunciation Key 
Symbol Pt
A soft, ductile, malleable, silver-white metallic element that usually occurs with osmium, iridium, palladium, or nickel. It has a high melting point and does not corrode in air. Platinum is used as a catalyst and in making jewelry, electrical contacts, and dental crowns. Atomic number 78; atomic weight 195.08; melting point 1,772°C; boiling point 3,827°C; specific gravity 21.45; valence 2, 3, 4. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
These rods are made of copper, and are platinum-tipped and gold-plated.
The idea is that all of the platinum-level technology could be added to the other building at some point in the future.
He was pale pink, with poker-straight reddish-brown hair that later grew into platinum-blonde curls.
Suddenly these megawatt music efforts stopped achieving multi-platinum success.
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