dalton [John Dalton, English chemist and mathematician, 1766–1844] , 1. an unofficial unit of atomic mass that was based on 1/16 of the gram mass of oxygen until 1961; it is now based on 1/12 the mass of carbon-12. Also called atomic mass unit. 2. (in biochemistry) unit (kilodaltons) that expresses the molecular weight (mass) of proteins and nucleic acids.
