The Nernst coefficient for the quasi-one-dimensional metal, Li{0.9}Mo{6}O{17}, is found to be among the largest known for metals (ν≃500 μV/KT at T∼20 K), and is enhanced in a broad range of temperature by orders of magnitude over the value expected from Boltzmann theory for carrier diffusion. A comparatively small Seebeck coefficient implies that Li{0.9}Mo{6}O{17} is bipolar with large, partial Seebeck coefficients of opposite sign. A very large thermomagnetic figure of merit, ZT∼0.5, is found at high field in the range T≈35-50 K.