tracer

noun

trac·​er ˈtrā-sər 

1

: one that traces, tracks down, or searches out: such as

a

: a person who traces missing persons or property and especially goods lost in transit

b

: an inquiry sent out in tracing a shipment lost in transit

2

: one who traces designs, patterns, or markings

3

: a device (such as a stylus) used in tracing

4

a

: ammunition containing a chemical composition to mark the flight of projectiles by a trail of smoke or light

b

: a substance used to trace the course of a chemical or biological process

especially : label sense 1d

Examples of tracer in a Sentence

The enemy fired tracers at the aircraft carrier.

They injected her with a radioactive tracer and tracked it via X-rays.

Recent Examples on the Web

The dye, a non-toxic tracer often used in environmental studies, transformed the waters of the Grand Canal into a bright green color. —Julia Jacobo, ABC News, 25 Nov. 2025

Extinction Rebellion said the dye used was a fluorescent, non-toxic tracer commonly employed in environmental studies, such as tracking water flows or monitoring leaks. —Emma Bussey, FOXNews.com, 25 Nov. 2025

In fact, Elsbeth overhears Reynolds paying close attention to a concerned skip tracer (a new-to-me term for a process server) who brings them his worry that Anders is missing in the first place. —Sophie Brookover, Vulture, 14 Nov. 2025

During the scan, a small dose of the Tc99m-PYP tracer is infused into a person's arm vein. —Colleen Doherty, Verywell Health, 13 Nov. 2025

Word History

First Known Use

14th century, in the meaning defined at sense 1

Rhymes for tracer

• acer
• baser
• chaser
• pacer
• racer
• spacer
• eraser
• replacer
• radiotracer

Kids Definition

tracer

noun

trac·​er ˈtrā-sər 

1

a

: a person who traces missing persons or property

b

: an inquiry sent out in tracing a shipment lost in transit

2

a

: ammunition containing a chemical composition to mark the flight of projectiles by a trail of smoke or fire

b

: a substance and especially a labeled element or atom used to trace the course of a chemical or biological process

Medical Definition

tracer

noun

trac·​er ˈtrā-sər 

: a substance used to trace the course of a process

specifically : a labeled element or atom that can be traced throughout chemical or biological processes by its radioactivity or its unusual isotopic mass