- A unit of measurement which is not itself defined in terms of other units, and from which other units may be derived.
- Synonym: fundamental unit
- The SI unit of velocity is metres per second, derived from the base units metre and second.
- The main unit of a computer or hi-fi system.
- When upgrading her computer she bought a new base unit but kept the screen, keyboard and mouse.
- (measurement) derived unit
a unit of measurement on which others are based