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

In the study, Perry’s team used metabolic tracers in mouse models of breast cancer and melanoma to learn how glucose—a nutrient that tumors use to fuel rapid cell division—is distributed when the body is active. —Avi Patel, Hartford Courant, 30 Jan. 2026

Dark oxygen landers The two landers will collect water samples, measure electrical activity around the nodules and introduce chemical tracers. —Georgina Jedikovska, Interesting Engineering, 20 Jan. 2026

As of Wednesday, contact tracers had not identified a single additional case. —Grant Stringer, Mercury News, 12 Jan. 2026

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

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