1. To incorporate into a compound a substance that is readily detected, such as a radionuclide, whereby its metabolism can be followed or its physical distribution detected. 2. The substance so incorporated.
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la·bel 'lā-bəl n a usu. radioactive isotope used in labeling
1) to distinguish (an element or atom) by using an isotope distinctive in some manner (as in mass or radioactivity) for tracing through chemical reactions or biological processes
2) to distinguish (as a compound or cell) by introducing a traceable constituent (as a dye or labeled atom)
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la·bel (laґbəl) 1. a mark, tag, or other characteristic that identifies something. 2. to provide something with such a characteristic.Medical dictionary. 2011.