Real Dictionary

platinum
colour: Platinum hair is very fair, almost white.
uncountable noun: Platinum is a very valuable, silvery-grey metal. It is often used for making jewellery.

platinum in American English
a silver-colored, malleable, ductile, metallic chemical element that is highly resistant to corrosion and tarnish, used as a chemical catalyst, for acid-proof containers, ignition fuses, jewelry, dental alloys, etc.: symbol, Pt; at. no., 78
designating a record, tape, disc, video, etc. which has registered sales of a specified number, as two million, or value, as $1,000,000
adjective: made of platinum
noun: 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 apparatu

platinum in British English
noun: 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, electroplat