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 researchers used positron emission tomography (PET) scans, along with a radioactive tracer to measure the production of a chemical called acetylcholine in the participants’ brains at the start and end of the study. —Korin Miller, SELF, 23 Oct. 2025

This study presents boron isotopes as in situ tracers for studying glass dissolution mechanisms, assisting in predicting contaminant releases during waste glass-aqueous solution interactions. —Prabhat Ranjan Mishra, Interesting Engineering, 16 Oct. 2025

The imaging technique relies on the use of a radioactive tracer and a special camera to make pictures of breast tissue. —Hannah Millington, MSNBC Newsweek, 3 Oct. 2025

Bradley had previously held a temporary position with the county as a contact tracer during the pandemic. —Lucas Robinson, San Diego Union-Tribune, 18 Sep. 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