Pronunciation: (trā'sur),[key] —n. 1. a person or thing that traces.
2. a person whose business or work is the tracing of missing property, parcels, persons, etc.
3. an inquiry sent from point to point to trace a missing shipment, parcel, or the like, as in a transportation system.
4. any of various devices for tracing drawings, plans, etc.
5. Also called trac'er ammuni"tion. ammunition containing a chemical substance that causes a projectile to trail smoke or fire so as to make its path visible and indicate a target to other firers, esp. at night.
6. the chemical substance contained in such ammunition.
7. a substance, esp. a radioactive one, traced through a biological, chemical, or physical system in order to study the system.