造字之初，都是一字一義的。文字使用之後，才有依本義延伸的「引伸義」，和依聲托事的「假借義」，而呈現一字多義的狀態。《說文解字》說解文字的方式，是依循造字的過程。首先說解字義，其次說解字形，其次說解字音。《說文》收錄9353字，其中一字一義者8413字，佔89.5%；一字多義者926字，佔9.90%。然則一字一義是《說文》釋義的常例，一字多義則是《說文》的變例。《說文》一字多義的，類型多種，有一曰類、聲訓類、稱引通人類、稱引方言類、稱引古書類、疊釋多義類等，本文就其變例中佔字最多，最具特色的「一曰類」與「疊釋多義類」為考察對象，分其細類，明其效用，每類各舉數例以相印證。全文分為五小節，第一節、前言，略說撰寫原委。第二節、《說文》說解字義之類型，綜述《說文》一字多義之六種類型。第三節、《說文》「一曰」釋義例舉要，綜述《說文》一曰例之八種異名，以及一曰類釋義之三種類型與作用。第四節、《說文》「疊釋多義」例舉要，綜述《說文》重疊、連續解釋多義，不稱「一曰」之五種類型與作用。第五節、結語，綜述本文之八點成果。

Originally, Chinese character was created to go along with only one meaning. The polysemys and homonyms are invented in practical writings from origin characters' extended meanings or phonetic borrowing. Shuowen Jiezi demonstrates Chinese characters according to the progress of characters' creation. It first explains the meaning of a character; then explains its construction; finally, its pronunciation. Shuowen Jiezi totally demonstrates 9353 characters: 8413 (89.5%) characters have only single meaning; 926 (9.90%) characters are polysemys or homonyms, which are the exceptions of Shuowen Jiezi. Polysemys and homonyms can be classified into six groups: Yiyu 一曰 [Homogeneity], Shengxun 聲訓 [Homonym], Chengyin Tongren 稱引通 人[From Expert], Chengyin Fangyan 稱引方言 [From Vernacular], Chengyin Gushu 稱引古書 [From Ancient Text] and Dieshi Duoyi 疊釋多義 [Homonym and Polysemy]. The essay will focus on two largest and most specific groups Yiyue and Dieshi Duoyi, and further assort these two groups into minor sorts to explain their function with examples. The essay is divided into five sections. The first section is an introduction of the writing motive. The second section clarifies Shuowen Jiezi's six groups of polysemys and homonyms. The third section synthetically explains the eight other titles of Yiyue and Yiyue's three methods of explaining characters with examples. The fourth section synthetically explains Dieshi Duoyi's five methods of explaining characters that different from Yiyue with examples. The final section is conclusion. It will address the achievement of this essay on eight aspects.