Derogatur legi, cum pars detrahitur; abrogatur legi, cum prorsus tollitur. To derogate from a law is to enact something contrary to it; to abrogate a law, is to abolish it entirely. Dig. 50, 16, 102. See 1 Bouv. Inst. n. 91.
A Law Dictionary, Adapted to the Constitution and Laws of the United States. By John Bouvier. Published 1856.