I'm not sure what your asking? I'll just explain the differences, I guess. Two is the number after one. It's used for counting. For example; I have two eyes. Double can be used to describe twice the amount. For example; A double scoop ice cream has two scoops of ice cream. It can also mean two of identical (or similar) things. For example; After being hit on the head, he saw double. Dual is most often used for describing something that has two dissimilar characteristics. For example; I have a Dual DVD and VHS player. Twin is used to describe two individuals born at the same time to the same mother. For example; My cousin Rita gave birth to twins. It can also be used figuratively to describe someone who looks very much like another. For example; He looked like he could be John's twin. A duplex is most often used to describe two homes that share a single wall. For example; I live in Unit B of a Duplex.

Actually the usage of those words is almost the same. TWO can be used as noun and an adjective, like "two days", "two of a kind". When you use TWO the corresponding word will be in its plural form. DOUBLE is an adjective too, which means consisting of two parts or things; twofold, like "double-sided", "double dutch" - ice cream's flavor. DUAL is also an adjective that means in two parts, it can be used like how you use DOUBLE, like "Dual Core" - computer's CPU, "Dual Personality". DUPLEX is a noun, especially US flat on two floors. TWIN can also be used as TWO, the only difference is that TWIN means having identical characteristics. Like "Twin Towers", "Beautiful twins".

Hi Petchy, this site explains the words http://thesaurus.com/browse/dual