The kilogram is defined in terms of three defining constants:
• a specific atomic transition frequency ΔνCs, which defines the duration of the second,
• the speed of light c, which when combined with the second, … 展开

The kilogram is the only base SI unit with an SI prefix (kilo) as part of its name. The word kilogramme or kilogram is derived from the French kilogramme, which itself was a learned coinage, prefixing the Greek stem of χίλιοι khilioi "a th… 展开