- noun a metal that has a high relative atomic mass and density and is toxic to humans, e.g. copper, lead and zinc
- A naturally occurring elemental metal with a high molecular weight.
- A metal which has a specific gravity greater than a given amount, such as 5. Examples include iron, gold, osmium, and iridium, each of which has a specific gravity of approximately 7.8, 19.3, 22.5, and 22.6, respectively.