1. a bullet or shell containing a pyrotechnic composition that burns during flight to show the projectile’s path
Usage: military
2. a radioactive isotope used to track the movement or location of a substance in biological or chemical processes
Usage: scientific; medical
3. a person whose job is to find someone or something that is missing

Examples

• The soldiers could see the tracer bullets streaking through the night sky.
• Doctors injected a radioactive tracer to monitor blood flow to the heart.
• The missing person’s family hired a professional tracer to locate their relative.
• She made a tracer of the map by placing thin paper over it and copying the lines.
• The tracer helped scientists track how nutrients moved through the plant.
• Military tracers leave a bright trail that helps gunners adjust their aim.
• The medical tracer revealed blockages in the patient’s arteries.