tracer

• POS: Noun
• HYPHEN: trac=er

CIDE DICTIONARY

tracer, n. 

•  One who, or that which, traces.  [1913 Webster]
•  A person engaged (esp. in the express or railway service) in tracing, or searching out, missing articles, as packages or freight cars.  [Webster 1913 Suppl.]
•  An inquiry sent out (esp. in transportation service) for a missing article, as a letter or an express package.  [Webster 1913 Suppl.]
•  a type of ammunition that emits light or smoke as it moves toward its target, providing a visible path of the projectile in flight so that the point of impact may be observed; -- called also tracer ammunition.  [PJC]
•  the chemical substance used in tracer ammunition to cause it to be visible in flight.  [PJC]
•  a chemical substance with properties, such as radioactivity or fluorescence, which make it easily measurable, used to observe the movements of chemically related substances through a biological, physical, or chemical system; -- in biochemistry, also called labeled compounds.

  "Radioactive tracers are used, for example, to measure the retention or distribution of residues of drugs after administration to an animal, to determine the type and rate of metabolism; also, to measure the rate of motion of molecules in electrophoresis or the leakage of small quantities of material from a container. Small fluorescent tracers may be attached in many cases to macromolecules such as proteins or nucleic acids, allowing the motions of such macromolecules to be easily observed by their acquired fluorescence, without appreciably changing their properties. In biological and biochemial systems the common radioactive isotopes used in tracers are carbon-14, tritium (hydrogen-3), sulfur-35, phosphorus-32, and iodine-131; other isotopes are also used, including non-radioactive isotopes such as carbon-13."  [PJC]

OXFORD DICTIONARY

tracer, n.
1 a person or thing that traces.
2 Mil. a bullet etc. that is visible in flight because of flames etc. emitted.
3 an artificially produced radioactive isotope capable of being followed through the body by the radiation it produces.

THESAURUS

tracer

alpha radiator, atom, atomic cocktail, atomic model, ball, bar shot, beta radiator, bird shot, buckshot, bullet, cannon shot, cannonball, case shot, cobalt, crossbar shot, duck shot, dumdum bullet, expanding bullet, fission products, fluorescent paint, gamma radiator, grape, grapeshot, ion, langrel shot, manstopping bullet, nuclear atom, nuclide, pellet, planetary shell, radiator, radioactive waste, radiocalcium, radiocarbon, radiocopper, radioelement, radioiodine, radioisotope, radiosodium, radiothorium, radium, radium dial, radium paint, rifle ball, round shot, shell, shot, shrapnel, slug, split shot, subshell, tagged atom, tagged element, tracer atom, tracer element, valence shell