fundamental unit
noun
1- one of a set of unrelated units of measurement, which are arbitrarily defined and from which other units are derived. For example, in the SI system the fundamental units are the metre, kilogram, and second.基本单位。
1.1
- a thing which is or is perceived as being the smallest part into which a complex whole can be analysed（构成复杂整体的）最基础单位, 最小单位：
the house is the fundamental unit of Basque society.
家庭是组成巴斯克社会的最基础单位。