noun a fundamental physical force that governs interactions between hadrons and leptons (as in the emission and absorption of neutrinos) and is responsible for particle decay processes (as beta decay) in radioactivity, that is 10-5 times the strength of the strong force, and that acts over distances smaller than those between nucleons in an atomic nucleus — called also weak interaction, weak nuclear force — compare electromagnetism 2a, gravity 3a(2), strong force