Though the importance of the lexical education has long been emphasized in the Korean language education, often it does not turn out true when borrowing the arguments which have been set out by the Korean academic circles as it is. Especially, the arguments on the synonym, a lexical set similar in its meaning, should be started from the awareness of the problems that they should be widely defined and studied in the Korean language education. The Korean academic circles have regarded the synonyms as a pair or a set of vocabularies, largely focusing on their semantic similarities. However, phonemes, forms, grammar, pragmatics, and synonyms in lexical relations as well as semantics should be studied in the Korean language education, because foreign learners of Korean language may experience learning disorder since they consider the vocabularies which have similar phonemes, forms, grammar, pragmatics, etc. as the synonyms. This thesis has identified the differences in the semantics of psychological adjectives which have many synonyms, based on the study by Hyunkyung Yoo and Hyounhwa Kang(2000) who established the extended notion of synonyms. Though it is not easy to discern the differences among these vocabularies because the psychological adjectives have a strong semantic contiguity and syntactic similarity among many synonyms in the lexical relation, this study proceeded a discussion for 4 vocabularies {기쁘다, 즐겁다, 재미있다, and 행복 하다} of high frequency, which are listed in Korean Textbook Beginners’ Level among the vocabularies belonging to the same emotional area with ‘기 쁨(joy)’ and defined as the extended notion of synonym to ‘기쁘다’. This thesis has identified the semantic differences of the synonyms in the lexical relation, suggesting that the position of synonyms which has been argued by the Korean academic circles should be the extended notion of synonyms in the Korean language education. There are two limitations: the range of the extended notion of synonyms with which this study has dealt is not wide enough, and the link between the results of the study and the Korean language education is weak. However, since there are significantly many synonyms that could be linked extendedly among the Korean vocabularies, it is expected that the subsequent efforts would be continued to set up the relationship between these vocabularies in accordance with the Korean language education and apply the error analysis or study of collocations to it. (Hankuk University of Foreign Studies)