With a particular focus on the combining forms and productivity, this paper traces the history of 三 sān (“three”) used as cardinal numbers and examines the semantic variation of 三 sān (“three”) in its indefinite meaning. Two levels of productivity are utilized in the current study. One is productivity at the lexical level, which indicates the ability for a simple word like 三 sān (“three”) to make compounds or phrases, a phenomenon really prevalent in Chinese. The other is productivity at the semantic level, which evaluates the productivity of a certain meaning of one word. The results observe a decrease in the indefinite usage of 三 sān (“three”) and its combining forms as well as some mechanisms of semantic change concerning metonymy, analogy, heterosemy, and metaphor.