New name for degree Kelvin (°K), temperature scale that begins at absolute zero (-273.15°C) and increases by one kelvin which is equal to one degree Celsius (1°C). On this scale, water freezes at 273.15 kelvin and boils at 373.15 kelvin. Named after Irish physicist William Thomson (1824-1907) who was honored as 1st Baron Kelvin (Lord William Kelvin).