n 1  :  a quality imparted to voiced sounds by vibration in anatomical resonating chambers or cavities (as the mouth or the nasal cavity)  2  :  the sound elicited on percussion of the chest  3  :  the conceptual alternation of a chemical species (as a molecule or ion) between two or more equivalent allowed structural representations differing only in the placement of electrons that aids in understanding the actual state of the species as an amalgamation of its possible structures and the usu. higher-than-expected stability of the species  4 a  :  the enhancement of an atomic, nuclear, or particle reaction or a scattering event by excitation of internal motion in the system  b  :  MAGNETIC RESONANCE - see ELECTRON SPIN RESONANCE  .
 
   
 
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