General Definition: 1. A thing or quantity which is of a defined and relatively small size, extent or duration or any thing or quality that can easily be associated with this in context. As a Noun: 1. A single complete thing. English = unit. 2. A single thing which is a part of a larger thing. English = unit, component. 3. A fixed, standard quantity, length, or weight that is used for measuring things. The metre, the litre, and the gram are all examples. English = unit.