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The description of the word you requested from the astronomical dictionary is given below.
In astronomy, a resonance is a case where small effects that can usually be ignored now do have a measurable impact because they happen exactly in step with something else. An orbit-orbit resonance occurs, for example, when a multiple of the orbital period of a moon is equal to the orbital period of another moon, or a multiple of it. A spin-orbit resonance occurs, for example, when a multiple of the spin period of a moon (around its own axis) is equal to the orbital period of the moon, or a multiple of it.