Magnetic circular dichroism (MCD) and absorption spectra are reported for the CH (methylidyne or methyne) free radical isolated in an Ar matrix (CH/Ar) over the temperature range 1.4-15.9 K and the magnetic-field range 0-4 T. Data for the A (2) Delta <-- X (2) Pi, B (2) Sigma(-) <-- X (2) Pi, and C (2) Sigma(+) <-- X (2) Pi band systems indicate a substantial quenching of the orbital angular momentum of the CH ground-state term. This is interpreted as being a consequence of crystal-field interactions involving atoms of the host lattice. Analysis of the zeroth moments of the spectra yields an empirical spin-orbit coupling constant A(Pi) = 21 +/- cm(-1) and orbital reduction factor kappa = 0.26 +/- 0.03, corresponding to a crystal-field splitting of V-Pi = 78 +/- 14 cm(-1) for the X (2) Pi term. For the A (2) Delta excited-state term, the first MCD moments give A(Delta) = 5 +/- 1 cm(-1), and an upper limit of V-Delta less than or similar to 15 cm(-1) is estimated from the dispersion of the MCD.