ETYM Abbrev. from unity.
(quantity) Standard quantity in relation to which other quantities are measured. There have been many systems of units. Some ancient units, such as the day, the foot, and the pound, are still in use. si units, the latest version of the metric system, are widely used in science.
1. A single undivided natural entity occurring in the composition of something else; SYN. building block.
2. A single undivided whole.
3. An individual or group or structure or other entity regarded as a structural or functional constituent of a whole.
4. An organization regarded as part of a larger social group; SYN. social unit.

Being, relating to, or measuring one unit

In warfare, another name for a battalion.