noun

• (chemistry) A compound, element, or isotope used to track the progress or history of a natural process.
• A round of ammunition for a firearm that contains magnesium or another flammable substance arranged such that it will burn and produce a visible trail when fired in the dark.
• The act or state of tracking or investigating something.
• A request to trace the movements of a person or an object, such as a shipment.
• A person who traces something.
• A device or instrument used to assist in making tracings.