The CCFR collaboration reports a precise measurement of electroweak parameters derived from the ratio of neutral-current to charged-current cross-sections in neutrino-nucleon scattering at the Fermilab Tevatron. We determine sin2 θ(on-shell)W = 0.2236 ± 0.0028 (expt.) ± 0.0030 (model) for Mtop = 175 GeV, MHiggs = 150 GeV. This is equivalent to MW = 80.35 ± 0.21 GeV. The good agreement of this measurement with Standard Model expectations implies the exclusion of additional vvqq contact interactions at 95% confidence at a mass scale of 1-8 TeV, depending on the form of the contact interaction.