1. An individual, group, structure, or other entity regarded as an elementary structural or functional constituent of a whole.
2. A group regarded as a distinct entity within a larger group.
a. A mechanical part or module.
b. An entire apparatus or the equipment that performs a specific function.
4. A precisely specified quantity in terms of which the magnitudes of other quantities of the same kind can be stated.
5. Medicine The quantity of a vaccine, serum, drug, or other agent necessary to produce a specific effect.
a. A fixed amount of scholastic study used as a basis for calculating academic credits, usually measured in hours of classroom instruction or laboratory work.
b. A section of an academic course focusing on a selected theme: a unit on Native Americans.
7. The number immediately to the left of the decimal point in the Arabic numeral system.
a. The lowest positive whole number; one.
b. An element of a ring with a multiplicative inverse.
[Back-formation from UNITY.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.