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We report time-domain THz spectroscopy measurements of α-RuCl₃ as a function of temperature and applied in-plane magnetic field, H, in the energy range 0.3 to 8.3 meV. Polarized measurements show that at zero field, 3-fold rotational symmetry is broken in the honeycomb plane from 2 K to 300 K. Below T_N, and with B(t) parallel H, we observe an antiferromagnetic resonance (AFMR) peak at 2.56 meV atop a large broadband continuum which can attributed largely to electric dipole absorption. We track the evolution of the AMFR peak from H = 0 T to 7 T as it broadens and shifts to lower frequency. From spectral weight analysis of this peak, we place an upper bound on the contribution to the dc susceptibility from a magnetic excitation continuum. Ref. arxiv:1704.07357