noun

1. the quality or state of being resonant
2. reinforcement and prolongation of a sound or musical tone by reflection or by sympathetic vibration of other bodies
3. 1. the quality of having an intensity of emotion or richness of expression that evokes or reinforces a sympathetic response
   2. an underlying or pervasive quality of a particular type, esp. in a work of art or literature an apocalyptic resonance
4. Chem. the property of certain molecules of having two or more structures in which only the positions of electrons differ: these structures are approximations of the true structure, which cannot be described graphically, but is best represented by a mathematical expression
5. Elec. a condition arising in an electric circuit in which
   1. the current or voltage flow is at maximum amplitude, produced when the frequency of the electrical source is varied, or
   2. the current or voltage is in phase respectively with the applied current or voltage, or
   3. the natural frequency of the circuit is the same as that of the incoming signal
6. Med. the sound produced in the percussion of some part of the body, esp. of the chest
7. Physics
   1. the effect produced when the amplitude of oscillation of a body is greatly increased by a periodic force at the same or nearly the same frequency
   2. a vibration caused by this phenomenon
8. Phonet. the intensification of, and particular quality given to, a speech sound, resulting from its vibrating in a resonating cavity, as the pharynx, the mouth, or the nose, or a combination of these

Etymology: LME resonnaunce < MFr resonance < L resonantia, an echo