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

Neither case caused outbreaks, because vaccination rates are high enough that the virus couldn’t get a toehold in the population, experts said, and teams of contract tracers quickly identified the scope of exposures and notified the public. —Grant Stringer, Mercury News, 27 Feb. 2026

The talc was Katharine’s visual tracer. —Natalia Sánchez Loayza, Scientific American, 26 Feb. 2026

To study crowding in cells, biologists needed a proxy molecule in the same size range — a tracer roughly as large as the large molecules involved in most cellular reactions. —Quanta Magazine, 18 Feb. 2026

The PET scan uses a radioactive drug called a tracer to show both typical and atypical metabolic activity, according to the Mayo Clinic. —Stephanie Giang-Paunon, FOXNews.com, 18 Feb. 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