Definition of "tracer" []

• One who is employed to locate missing goods or persons. (noun)
• An investigation or inquiry organized to trace missing goods or persons. (noun)
• Any of several instruments used in making tracings or in imprinting designs by tracing. (noun)
• A tracer bullet. (noun)
• An identifiable substance, such as a dye or a radioactive isotope, that is introduced into a biological or mechanical system and can be followed through the course of a process, providing information on the pattern of events in the process or on the redistribution of the parts or elements involved. Also called label. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The set of delayed images will begin anywhere from 2 to 4 hours after the tracer is given."
• "The pharmaceutical or medicine portion of the tracer is designed to travel to a particular organ or area of the body."
• "Bursts of yellow tracer from the German machine guns pursued the fleeing gun crews."