base unit

/B EY1 S Y UW0 N AH0 T/
noun
  1. 1

    A unit of measurement on which others are based.

    โ€œThe SI unit of velocity is metres per second, derived from the base units of time and distance.โ€

  2. 2

    The main unit of a computer or hi-fi system.

    โ€œWhen upgrading her computer she bought a new base unit but kept the screen, keyboard and mouse.โ€

Antonyms

Source: https://en.wiktionary.org/wiki/base%20unit