tracer

American  

[trey-ser] / ˈtreɪ sər /

noun

1. a person or thing that traces.

2. a person whose business or work is the tracing of missing property, parcels, persons, etc.

3. an inquiry sent from point to point to trace a missing shipment, parcel, or the like, as in a transportation system.

4. any of various devices for tracing drawings, plans, etc.

5. Also called tracer ammunition.  ammunition containing a chemical substance that causes a projectile to trail smoke or fire so as to make its path visible and indicate a target to other firers, especially at night.

6. the chemical substance contained in such ammunition.

7. a substance, especially a radioactive one, traced through a biological, chemical, or physical system in order to study the system.

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tracer British  

/ ˈtreɪsə /

noun

1. a person or thing that traces

2. 1. a projectile that can be observed when in flight by the burning of chemical substances in its base

   2. ammunition consisting of such projectiles

   3. ( as modifier )

      tracer fire

3. med any radioactive isotope introduced into the body to study metabolic processes, absorption, etc, by following its progress through the body with a gamma camera or other detector

4. an investigation to trace missing cargo, mail, etc

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tracer Scientific  

/ trā′sər /

1. An identifiable substance, such as a dye or radioactive isotope, that can be followed through the course of a mechanical, chemical, or biological process. Tracers are used in radioimmunoassays and other laboratory testing. The use of radioactive iodine, for example, can give information about thyroid gland metabolism.

2. Also called label

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Etymology

Origin of tracer

First recorded in 1535–45; trace ¹ + -er ¹

Example Sentences

A review of several studies found that the average cost per measles case is $43,203, and each person who has to be notified by a contact tracer after exposure costs $443.

From MarketWatch • Dec. 17, 2025

Overnight, AFP journalists saw Ukraine using tracer bullets and missile defence systems, and incandescent debris falling over large areas above the capital.

From Barron's • Nov. 14, 2025

One head described it as a "tracer" letter, asking principals if any of the named pupils have subsequently enrolled in a different school.

From BBC • Oct. 16, 2025

It took about an hour on a weeknight after work, and afterward, Gluck made a throwaway joke to the technician: Am I glowing from the radioactive tracer?

From Slate • May 2, 2025

On occasion, when they were taken under fire, Mary Anne would stand quietly and watch the tracer rounds snap by, a little smile at her lips, intent on some private transaction with the war.

From "The Things They Carried" by Tim O'Brien