  The spectral properties of a hybrid steady thermal-nonthermal isotropic
plasma are studied. The involved emission mechanisms are thermal
bremsstrahlung, nonthermal bremsstrahlung, cyclotron and nonthermal
synchrotron. Formulas are derived to calculate the emissivities and absorption
coefficients of all these processes. Calculations show that the nonthermal
synchrotron and the thermal bremsstrahlung dominate over most of the frequency
range and that the cyclotron and the nonthermal bremsstrahlung are important
only at the two ends of the spectrum. The combination of the two dominant
processes could generate the synchrotron self-absorbed spectrum, the
Rayleigh-Jeans spectrum and an absorbed flatter spectrum which is seen in some
solar flare radio spectra. Absorbed spectra steeper than the three types of
spectra are rare. The conditions for these three possible spectral types are
given. Cyclotron harmonic features are seen in the emergent spectra from the
hybrid plasmas. These harmonic features, useful in determining the magnetic
field, exist only under certain conditions which are explored in this paper.
