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

But this lower end of the galactic scale is still rather murky, in part because the stars that serve as observable tracers of small galaxies can form even smaller structures called star clusters. —Phil Plait, Scientific American, 8 May 2025

Contact tracers tried to identify everyone exposed and figure out where the virus might have come from. —Kelsey Piper, Vox, 8 May 2022

The physical tracer in Recover fibers means the final garment can be verified using a scanner. —Angela Velasquez, Sourcing Journal, 22 Apr. 2025

If the rhythmic releases of norepinephrine correlate with the arrival of a larger tracer at a sensor on the brain’s surface, that would be a fascinating finding. —Veronique Greenwood, Quanta Magazine, 26 Mar. 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