trace element 
noun
1A chemical element present only in minute amounts in a particular sample or environment.Also, aragonite tends to have much higher amounts of strontium as a trace element in the calcium carbonate....
- It was later identified that molybdenum was the most abundant trace element present in the soluble and insoluble extractions of the wood-ash.
- The trace element and isotopic characteristics of these dykes imply derivation from an asthenospheric mantle source, which is likely to occur only as a result of regional lithospheric extension.
1.1A chemical element required only in minute amounts by living organisms for normal growth.It crops up in milk of magnesia, and as Epsom salts (magnesium salts are catastrophically laxative…), but it is also an essential trace element, required for the normal function of virtually every organ....
- A diet high in sugar can deplete your body's supply of chromium, a trace element responsible for helping insulin transport glucose into cells and for aiding the cellular uptake of amino acids into your system.
- Selenium is a trace element and is found as a component of several prokaryotic and eukaryotic enzymes that are involved in redox reactions.