The word "大厦" is formed by combining two characters, each contributing its core meaning to create a new, composite concept. The first character, "大" (dà), carries the fundamental meaning of "big" or "large". The second character, "厦" (shà), specifically means "a tall building" or "mansion". Therefore, when joined, they semantically compound to directly denote a "large building", with the modern connotation specifically pointing to a grand, imposing structure, typically a tall commercial or residential edifice.