The word "熙来攘往" is formed by pairing two antithetical phrases: "熙来" (bustling come) and "攘往" (jostling go), where the characters "熙" and "攘" both denote bustling activity, while "来" and "往" are opposing directional verbs meaning "to come" and "to go", collectively creating a compound that vividly depicts continuous, busy movement of people.