tracer

trac·er

noun \ˈtrā-sər\

: a type of bullet that shows its path by creating smoke or light as it moves through the air

medical : a substance that is put in a patient's body so that doctors can watch a biological process (such as digestion) or see how a condition (such as cancer) is progressing

Full Definition of TRACER

1

:  one that traces, tracks down, or searches out: 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 (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 3d

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Examples of TRACER

1. The enemy fired tracers at the aircraft carrier.
2. They injected her with a radioactive tracer and tracked it via X-rays.

First Known Use of TRACER

14th century

Rhymes with TRACER

bracer, chaser, facer, pacer, placer, racer, spacer

trac·er

noun \ˈtrā-sər\   (Medical Dictionary)

Medical Definition of TRACER

: 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