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

More contact tracers would help, and the World Health Organization (WHO) announced that 21,000 community workers are being trained right now. — Jonathan Lambert, NPR, 23 July 2026

Scientists are now using advanced stable isotope ecology, moving beyond traditional carbon and nitrogen tracers, to unlock these secrets. — Melissa Cristina Márquez, Forbes.com, 11 July 2026

This imaging test uses a tracer that attaches to PSMA proteins, allowing doctors to identify where prostate cancer cells may be located throughout the body. — Lauryn Higgins, Flow Space, 15 June 2026

Many health care workers served longer, harder deployments than mine — Sierra Leonean nurses, Guinean contact tracers, Liberian community health workers — and carried equal or greater burdens, yet Americans rarely heard their stories. — Krutika Kuppalli, STAT, 20 May 2026

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