The crossword solution for the term COMPLEX PART is UNIT. A UNIT is a single element of a larger system or structure. It can refer to a physical object, such as a machine PART, or an abstract concept, such as a mathematical equation. Units are often used to measure and compare different aspects of a system, such as size, weight, or time. In mathematics, a UNIT is a number that is used to represent a certain quantity, such as one meter or one second. In engineering, a UNIT is a component of a larger system, such as a motor or a circuit. Units are also used in chemistry, biology, and other sciences to measure and compare different substances.