Shuowen Jiezi
Shuōwén Jiězì (Chinese: 說文解字; Wade–Giles: Shuo-wen chieh-tzu; literally "Explaining and Analyzing Characters"), often shortened to Shuowen, was an early 2nd century Chinese dictionary from the Han Dynasty. Although not the first comprehensive Chinese character dictionary (the Erya predates it), it was still the first to analyze the structure of the characters and to give the rationale behind them (sometimes also the etymology of the words represented by them), as well as the first to use the principle of organization by sections with shared components, called radicals (bùshǒu 部首, lit. "section headers").
Read more about Shuowen Jiezi: Circumstances of Compilation, Textual Organization, Contents and Importance, Textual History and Scholarship