The noun unit has 6 senses (first 5 from tagged texts)
1. (34) unit of measurement, unit -- (any division of quantity accepted as a standard of measurement or exchange; "the dollar is the United States unit of currency"; "a unit of wheat is a bushel"; "change per unit volume")
2. (16) unit -- (an individual or group or structure or other entity regarded as a structural or functional constituent of a whole; "the reduced the number of units and installations"; "the word is a basic linguistic unit")
3. (9) unit, social unit -- (an organization regarded as part of a larger social group; "the coach said the offensive unit did a good job"; "after the battle the soldier had trouble rejoining his unit")
4. (6) unit -- (a single undivided whole; "an idea is not a unit that can be moved from one brain to another")
5. (2) unit, building block -- (a single undivided natural thing occurring in the composition of something else; "units of nucleic acids")
6. whole, unit -- (an assemblage of parts that is regarded as a single entity; "how big is that part compared to the whole?"; "the team is a unit")