Precise measurement of the refractive index of chemical vapor deposition (CVD) ZnSe with the Fourier-transform interference refractometry method from 0.9 to $21.7\mathrm{\mu m}$ (from 11,000 to $460{\mathrm{cm}}^{-1}$ ) with $0.1{\mathrm{cm}}^{-1}$ 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 $2\times {10}^{-5}$ (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 $12.5\mathrm{\mu m}$ (wavenumber range of $11,000–800{\mathrm{cm}}^{-1}$ ) and up to $1\dots 4\times {10}^{-4}$ in the $12.5–21.7\mathrm{\mu m}$ ( $800–460{\mathrm{cm}}^{-1}$ ) 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 ${\lambda }_0=4.84\mathrm{\mu m}$ .