A single thing or person.
- An individual, group, structure, or other entity regarded as an elementary structural or functional constituent of a whole.
- A group regarded as a distinct entity within a larger group.
- A mechanical part or module.
- An entire apparatus or the equipment that performs a specific function.
- A precisely specified quantity in terms of which the magnitudes of other quantities of the same kind can be stated.
- Medicine The quantity of a vaccine, serum, drug, or other agent necessary to produce a specific effect.
- A fixed amount of scholastic study used as a basis for calculating academic credits, usually measured in hours of classroom instruction or laboratory work.
- A section of an academic course focusing on a selected theme: a unit on Native Americans.
- The number immediately to the left of the decimal point in the Arabic numeral system.
- Mathematics The lowest positive whole number; one.
- Mathematics An element of a ring with a multiplicative inverse.