This paper proposes a method to describe conceptual meanings of Japanese deverbal nouns for the purpose of analysing Japanese compound nouns. A lexical meaning of each constituent word is very important since it deeply influences a word formation of compound words. Therefore we intend to use the lexical meanings of constituent words to build a Japanese compound noun analyzer. As a first step to describe lexical meanings of words, we have established a simple semantic structure based on lexical conceptual structure (we refer to the structure we establish by TLCS in this paper). After the analysing 250 deverbal nouns that appeared in technical terms, we found that the only 14 types of TLCSes cover various deverbal nouns. We will explain in this paper the types of TLCS and also show the procedure of assigning TLCSes to deverbals. In order to evaluate the efficacy of TLCS, we made use of the accuracy of simple compound noun analyser for analyzing technical terms. The result was very good, which shows that our proposed method is very promising.