tracer
noun/ˈtreɪsə(r)/
/ˈtreɪsər/
- a bullet or shell (= a kind of bomb) that leaves a line of smoke or flame behind it
- tracer bullets
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- (specialist) a radioactive substance that can be seen in the human body and is used to find out what is happening inside the body
- Radioactive tracers have been used to map the metabolic activity of the brain.
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