ETYM French métal, Latin metallum metal, mine, Greek metalon mine. Related to Mettle, Medal.
(Homonym: mettle).
An opaque lustrous elemental chemical substance that is a good conductor of heat and electricity and, when polished, a good reflector of light; most elemental metals are malleable, ductile, and are generally denser than the other elemental substances; metals are structurally distinguished from nonmetals by their atomic bonding and electron availability; the electron band structure of metals is characterized by a partially filled valence band; the lost from the outer shells of metallic atoms are available to carry an electric current; the defining property of a metal is that it is an element with a positive thermal coefficient of resistivity, meaning the electrical resistivity of a metal continuously increases as temperature increases.
Any of a class of chemical elements with certain chemical characteristics (metallic character) and physical properties: they are good conductors of heat and electricity; opaque but reflect light well; malleable, which enables them to be coldworked and rolled into sheets; and ductile, which permits them to be drawn into thin wires.
Metallic elements compose about 75% of the 109 elements shown in the periodic table of the elements. They form alloys with each other, bases with the hydroxyl radical (OH), and replace the hydrogen in an acid to form a salt. The majority are found in nature in the combined form only, as compounds or mineral ores; about 16 of them also occur in the elemental form, as native metals. Their chemical properties are largely determined by the extent to which their atoms can lose one or more electrons and form positive ions (cations).
Metals have been put to many uses, both structural and decorative, since prehistoric times, and the Copper Age, Bronze Age, and Iron Age are named for the metal that formed the technological base for that stage of human evolution.
All metals, with the exception of mercury, are solid at ordinary temperatures, and all of them will crystallize under suitable conditions. The chief chemical properties of metals include their strong affinity for certain nonmetallic elements, e.g. sulfur, chlorine, and oxygen, with which they form sulfides, chlorides, and oxides. Metals will, when fused, enter into the forming of alloys. Many of the metals can decompose water or steam with the production of hydrogen.

To cover with metal.