(n)(cosmology) the ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer; the Hubble constant is not actually a constant, but is regarded as measuring the expansion rate today, Syn.Hubble's parameter, Hubble constant, Hubble parameter
(n)(astronomy) the generalization that the speed of recession of distant galaxies (the red shift) is proportional to their distance from the observer, Syn.Hubble law