Precise measurement of the refractive index of chemical vapor deposition (CVD) ZnSe with the Fourier-transform interference refractometry method from 0.9 to 21.7microm (from 11,000 to 460cm(-1)) with 0.1cm(-1) resolution is described. For this measurement, structurally homogeneous ZnSe plates were grown on a substrate with an optimized temperature increase. Using three ZnSe plates of different thicknesses, we managed to raise the measurement accuracy of the refractive index up to 2x10(-5) (being nearly 1 order of magnitude better than the available data) in the near IR and most of the middle IR wavelength range from 0.9 to 12.5microm (wavenumber range of 11,000-800cm(-1)) and up to 1...4x10(-4) in the 12.5-21.7microm (800-460cm(-1)) region. The experimental results are approximated by a generalized Cauchy dispersion function of the 8th power. Spectral wavelength dependencies of the first- and second-order derivatives of the refractive index are calculated, and the zero material dispersion wavelength is found to be lambda(0)=4.84microm.