What is the definition of dual?

The definition of "dual" is indeed best captured by the concept of "consisting of two parts." The word itself derives from the Latin term "dualis," which specifically refers to something that pertains to or is characterized by two elements. In various contexts, such as language, mathematics, or physical objects, duality signifies the existence or involvement of two distinct but interconnected components. This can pertain to concepts that serve a dual purpose, dual roles, or systems that operate on the basis of two foundational elements.

In contrast, the other definitions do not align with the meaning of "dual." The notion of being composed of a single part contradicts the essence of duality, which explicitly involves two. Similarly, being dependent on others or occurring only once diverges from the core idea of two simultaneous aspects or functions. These definitions do not accurately represent the term "dual" and thus affirm why "consisting of two parts" is the precise encapsulation of its meaning.