  We report the discovery of the partially eclipsing binary LP 133-373. Nearly
identical eclipses along with observed photometric colors and spectroscopy
indicate that it is a pair of chromospherically active dM4 stars in a circular
1.6 d orbit. Light and velocity curve modeling to our differential photometry
and velocity data show that each star has a mass and radius of 0.340+/-0.014
M_sun and 0.33+/-0.02 R_sun. The binary is itself part of a common proper
motion pair with LP 133-374 a cool DC or possible DA white dwarf with a mass of
0.49-0.82 M_sun, which would make the system at least 3 Gyr old.
