This study investigates the synonymic relationship between form and meaning in modern times Sino-Korean and Sino-Japanese, and aims to clarify usages found in each language. Although various different publications exist, this research selected as the subject material the 'Ineodaebang' (Meiji 1882 publication), as it is the closest to the current language. The contents of this research are composed of letters and recorded dialogues between Korean and Japanese people. As the scope of this research is limited to the analysis of three out of the nine volumes, the discussion is limited to the heteromorphic synonymy - where the form is different but the meaning is the same - used in both Korea and Japan at the time. The study confirmed the presence of 91 synonymic pairs in all 21 categories present in the three volumes, and results showed that bi-syllabic synonymic Sino-words appeared the most at 86%, and the appearance of “AB/CD” type words was found to be 38%. We were able to verify semantic reduction and widening, raising and lowering, as well as changes in meaning according to synonymic competition as a semantic phenomenon that appears in the synonymic Sino-words of Korea and Japan at the time. Through this research, we were able to re-establish the exchange between Sino-Korean and Sino-Japanese words, and it is our belief that this research will serve to assist scholars studying Korean and Japanese in the future. (Kansai University)