• WordNet 3.6
    • n tracer ammunition whose flight can be observed by a trail of smoke
    • n tracer (radiology) any radioactive isotope introduced into the body to study metabolism or other biological processes
    • n tracer an instrument used to make tracings
    • n tracer an investigator who is employed to find missing persons or missing goods
    • ***
Webster's Revised Unabridged Dictionary
    • Tracer 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.
    • Tracer A person engaged (esp. in the express or railway service) in tracing, or searching out, missing articles, as packages or freight cars.
    • Tracer (Mil) 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.
    • Tracer An inquiry sent out (esp. in transportation service) for a missing article, as a letter or an express package.
    • n Tracer One who, or that which, traces.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.
    • Tracer (Mil) the chemical substance used in tracer ammunition to cause it to be visible in flight.
    • ***
Century Dictionary and Cyclopedia
    • n tracer In ordnance, an attachment, to a projectile for use at night, provided with a burning composition by means of which, when the projectile is fired from a gun, its path throngh the air is rendered visible.
    • n tracer One who or that which traces, in any sense.
    • n tracer A small slender steel instrument, having a handle in the middle and its ends pointed more or less, and one of them usually also curved and edged, used in dissection as a compromise between scalpel and probe for tracing out the course of nerves, vessels, etc. It is usually held like a pen, and may be pushed into or drawn through tissue, as desired. Also called seeker.
    • n tracer One whose duty it is to trace or search out missing articles, as railway-cars, milk-cans, or letters.
    • n tracer c) An inquiry sent out from a post-office, express-office, railway-station, or other establishment after some missing letter, package, car, etc.
    • n tracer One who copies or makes tracings of drawings, etc.
    • n tracer An instrument, like a stylus, for tracing drawings, etc., on superimposed paper.
    • n tracer A simple kind of pantograph.
    • n tracer A form of outline-or copying-machine. It consists essentially of a long bar balanced by means of a universal joint near one end. The longer arm is directed toward the drawing, design, or other work to be copied on a reduced scale, and the shorter arm carries a pencil. On moving the point of the long arm over the work, the pencil on the short arm reproduces a reduced copy of the work on paper held before it. By reversing the relative positions of the pointer and pencil, an enlarged copy may be made. Also called tracing-machine.
    • n tracer A tool, sometimes a small smooth-edged wheel set in a handle, by means of which a continuous line is impressed, as in ornamental metal-work.
    • ***


In literature:

That there tracer started to hum again soon after you was out for a while.
"Zero Data" by Charles Saphro
He saw the streaks of tracers going very wide.
"Astounding Stories of Super-Science, June, 1930" by Various
The tracer pellet scorched upward, impacted, against the hull of a flier.
"Slaves of Mercury" by Nat Schachner
Square into the oncoming plane the tracers poured.
"Aces Up" by Covington Clarke
Anyhow, he didn't swing any tracers after us.
"Take the Reason Prisoner" by John Joseph McGuire
We would suggest that you enter tracer with the postoffice department in endeavor to locate the package.
"The So-called Human Race" by Bert Leston Taylor
Tracer bullets sprayed all around it.
"The Invaders" by William Fitzgerald Jenkins
Dalgetty's belly muscles stiffened, waiting for the tracers to burn through him.
"The Sensitive Man" by Poul William Anderson
Pressing a button marked TRACER LIGHT, she left the set in operation and made her way up to the top floor of the apartment house.
"The Amazing Mrs. Mimms" by David C. Knight
Whether or not the tracer had anything to do with the final result I never knew.
"Belford's Magazine, Volume II, No. 8, January, 1889" by Various

In news:

Harmless tracer gasses to be released in Massachusetts subway stations, cars.
The attack ads arrive in the mailboxes of Florida voters and pierce the television airwaves with the rapidity of tracer bullets.
Nonsteady-State Three Compartment Tracer Kinetics.
Teengirl Fantasy EFX Tracer True Panther Sounds.
Keen, Tracer of Lost Persons.
The US Forest Service is warning shooters to avoid the use of tracer bullets after a small wildfire broke out over the weekend on the Eastern Plains.
If you don't know Tracer , you should even if they can't pull off the upset.
Tracer Release Music Video from New Album, Give Away $100 iTunes Gift Card.
PET Tracer Captures Astrocytosis in Alzheimer's Patients.
Audio Performer Tracer Technologies Inc. Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4.
He was a jeweler and owned Tracer 's Jewelry Store in Monette.
Tracer Utility Is Likely Culprit In Visas Fujitsu POS Security Alert.
Bessie Tracer , 98, of Rector, died Aug 12, 2005, at Arkansas Methodist Hospital in Paragould.
UCISCO, Tracer and Corrocon Join Forces to Become Praxair Services Inc.
REVIEWS Teengirl Fantasy, ' Tracer .

In science:

The most common tracer of the amount of circumstellar gas is CO.
The Very Slow Wind From the Pulsating Semiregular Red Giant L2 Pup
Thus, interstellar dust plays a most important role as a tracer of the distribution and of the structure of interstellar matter.
The incompatibilities between the standard theory of interstellar extinction and observations
It is also well known that Hα emission is a good tracer of current star formation.
Optical Counterparts of X-Ray Point Sources Observed by CHANDRA in NGC5128: 20 New Globular Cluster X-Ray Sources
The first is that a given potential well (as the one associated with the cluster DM distribution) can be filled, in principle, by very different distributions of “tracers” (such as the galaxies in the clusters, from which the scaling relations are derived).
The scaling relations of galaxy clusters and their dark matter halos
However, an obvious limitation is that these studies cannot predict the density of all types of stars in the solar neighborhood of the disk since they include only a single tracer population.
Dark Matter in the Local Galactic Disk