noun

• (uncountable) The quality of being resonant.
• (countable) A resonant sound, echo, or reverberation, such as that produced by blowing over the top of a bottle.
• (medicine) The sound produced by a hollow body part such as the chest cavity upon auscultation, especially that produced while the patient is speaking.
• (figuratively) Something that evokes an association, or a strong emotion; something that strikes a chord.
• (physics) The increase in the amplitude of an oscillation of a system under the influence of a periodic force whose frequency is close to that of the system's natural frequency.
• (nuclear physics) A short-lived subatomic particle or state of atomic excitation that results from the collision of atomic particles.
• An increase in the strength or duration of a musical tone produced by sympathetic vibration.
• (chemistry) The property of a compound that can be visualized as having two structures differing only in the distribution of electrons.
• (astronomy) An influence of the gravitational forces of one orbiting object on the orbit of another, causing periodic perturbations.
• (electronics) The condition where the inductive and capacitive reactances have equal magnitude.
• (sociology) A quality of human relationship with the world.