Dielectric study on Ca3Mn2O7 features relaxor-like segmented dynamics below the antiferromagnetic ordering. Dipolar relaxations of different origin are spectrally resolved exhibiting distinct H-field alterations. This identifies their allegiance to different magnetic sub-phases and establishes dual coupling of electrical, magnetic, and structural degrees of freedom. Further, strong spin-lattice coupling has been affirmed with Raman spectroscopy across the magnetic ordering. Short-range electrical correlations collaterally cause measurable harmonic dielectric response in the system. The c{hi}_3^e-susceptibility signal yields genuine harmonic magneto-dielectricity, consistent with but exhibiting two orders of magnitude larger H-field effect, vis-`a-vis that obtained in the fundamental dielectric constant {epsilon}.
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