Most software specifications are discussed on natural language among stakeholders. There is, however, a semantic gap between natural language and programming language, which sometime causes discrepancies between them and misunderstanding among stakeholders. Formal language compensates the gap so that realizes early verification in software development process. We developed a dictionary tool to support the translation from natural language to formal language. The tool provides functionalities those are easy registration of keywords to the dictionary and exhaustive marking of the keywords. The dictionary represents a map between equivalent keywords in natural language and formal language which gives defined semantics, and the tool enhance the coverage of the keywords in the formal specification. In short, the dictionary contains conceptual keywords and specific semantics in the problem; therefore, it corresponds to a domain of the system. A system generally belongs to multi problem domains and also contains multi sub domains, consequently some dictionaries should be dynamically alternated through the translation process. APIs related to dictionary operation are proposed and verified in this paper, and the dictionary class is introduced to map the relation among domains.