noun
tracer
TRAY-suh
noun
1
A substance, such as a radioactive isotope or dye, used to track how something moves or changes through a system.
"Doctors injected a radioactive tracer to follow blood flow through the heart."
2
A bullet or shell that leaves a visible trail of light so its path can be seen, especially at night.
"Tracer rounds lit up the night sky during the battle."
How to Use Tracer
Learner’s notesIn plain EnglishSomething used to track a path — either a marked substance followed through a body or system, or a glowing round of ammunition.
Common pairings
radioactive tracer
tracer bullet
tracer round
Word Forms
tracers plural
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Doctors injected a radioactive _____ to follow blood flow through the heart.