It is recommended that in handwritten material this word be written in full, because the abbreviation U is subject to frequent misinterpretation. (1) One; a single person or thing. (2) A standard of measure, weight, or any other quality, by multiplication or fractions of which a scale or system is formed. (3) A group of people or things considered as a whole because of mutual activities or functions.international unit. [L. unus, one]