The thermionic emission of a flat oxide cathode in a 3 torr argon DC discharge has been determined in the regime of moderate ion bombardment; that is, with relative ion currents of up to 15%. The electrode temperatures were about 1000K, the current densities were up to 2.5 A cm^-2. The work-function phi ₀ and the Richardson constant A_R, depend on the discharge current density j. At low discharge currents the electron current density at zero electric field at the cathode surface, j₀=A_Rexp(-e phi ₀/kT), is related to j as j₀ approximately=¹/₂j, and depends only sightly on the cathode temperature. The ion bombardment appears to activate the cathode in the gas discharge, and j₀ increases with higher discharge currents up to a temperature-dependent maximum j₀-value. This activation is reversible, which indicates a competing deactivation process at the cathode surface in the gas discharge. Still further increase of the discharge current leads to erosion of the cathode.