  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}'.
