horseradish peroxidase: an enzyme used in immunohistochemistry to label antigens and their antibodies
peroxidase: any of a group of enzymes (occurring especially in plant cells) that catalyze the oxidation of a compound by a peroxide
hubble's constant: (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