The word "主题" (zhǔtí) is formed through the direct conceptual combination of its two constituent characters: "主", which carries the core idea of "main", "primary", or "master", and "题", which represents "topic", "subject", or "title". Their union is not grammatical but ideographic, creating a compound where the first character modifies and elevates the second, synthesizing the abstract concept of a "main topic" or "central theme" as a single, unified idea.