This book focuses on two types of Middle Korean words, i.e. native Korean words and Sino-Korean words.

The original text of this book is the Middle Korean translation of the Thay-San-Cip-Yo (胎産集要), which was a medical book in the Joseon Dynasty. Dr. Yeong-Seop Park claims that medical books of those days provide linguists with materials important to a research of the Middle Korean language. This is based on the historical fact that in the Joseon Dynasty medical books written in classical Chinese were translated into one of the simplest words in order to teach even ordinary people medical knowledge. Moreover, this book selects the following texts as supplementary research materials: (1) an anthology Twu-Si-En-Hay (杜詩諺解) 'the Middle Korean translation of Po Twu (杜甫)’s poetry', (2) three Buddhist scriptures 'Sek-Po-Sang-Cel (釋譜詳節)', 'the Middle Korean translation of the Nung-Em-Kyeng (楞嚴經)', and 'the Middle Korean translation of the Nam-Myeng-Chen-Kyey-Song (南明泉繼頌)', (3) three handbooks of Chinese characters for children, i.e. 'Hwun-Mong-Ca-Hoy (訓蒙字會)', 'Yu-Hap (類 合)', and 'Chen-Ca-Mwun (千字文)'.

This book makes a comparative analysis on Middle Korean equivalents for Chinese characters of the main text, i.e. 'the Middle Korean translation of the Thaysancipyo', and the other texts. This analysis shows the following two results. One is how one Chinese character is translated into multiple Middle Korean native words according to contexts. The other is the phenomenon of disappearance of Middle Korean words. This phenomenon rose from the competitive relationship between/among synonymous Middle Korean native words or between/among synonymous Middle Korean native words and Middle Sino-Korean words.