Tracer

['treɪsə] or ['tresɚ]

(noun.) ammunition whose flight can be observed by a trail of smoke.

(noun.) (radiology) any radioactive isotope introduced into the body to study metabolism or other biological processes.

(noun.) an instrument used to make tracings.

(noun.) an investigator who is employed to find missing persons or missing goods.

卡特编辑--From WordNet

(n.) One who, or that which, traces.

校对:维托