  We present photometric and spectroscopic observations of a peculiar variable
(designated DASCH J075731.1+201735 or J0757) discovered from our DASCH project
using the digitized Harvard College Observatory archival photographic plates.
It brightened by about 1.5 magnitudes in B within a year starting in 1942, and
then slowly faded back to its pre-outburst brightness from 1943 to the 1950s.
The mean brightness level was stable before and after the outburst, and
ellipsoidal variations with a period of $P=119.18\pm0.07$ days are seen,
suggesting that the star is tidally distorted. Radial-velocity measurements
indicate that the orbit is nearly circular ($e=0.02\pm0.01$) with a
spectroscopic period that is the same as the photometric period. The binary
consists of a $1.1\pm0.3 M_\odot$ M0III star, and a $0.6\pm0.2 M_\odot$
companion, very likely a white dwarf (WD). Unlike other symbiotic binaries,
there is no sign of emission lines or a stellar wind in the spectra. With an
outburst timescale of ~10 years and estimated B band peak luminosity M_B~0.7,
J0757 is different from any other known classic or symbiotic novae. The most
probable explanation of the outburst is Hydrogen shell-burning on the WD,
although an accretion-powered flare cannot be ruled out.
