Requirement is a formal expression of user’s need. It is the main foundation of any software development project. Natural language (NL) is often used to express and write system requirements specifications as well as user requirements. However, there is a very high probability that more than half natural language requirements can be ambiguous, incomplete and inaccurate. A software engineer can miss-interpret the natural language requirements and can generate an erroneous software model, which finally will lead to project failure. Earlier, we have introduced a prototype tool that provides natural language requirements authoring facilities and consistency checking to assist requirement engineers when working with informal and semi-formal requirements. However, the tool has pattern limitation to support the extraction of the essential requirements from the NL requirements. Therefore this study is aimed to enhance the accuracy and scalability of the tool to capture the essential requirements from the NL requirements. Our approach is to implement lexical analysis and embed an English lexical database where it will serve as a thesaurus in the tool. This tool is expected to be able to find the synonym of the extracted phrases (essential requirements) in the database to match it to the essential interaction pattern (phrases and expressions) in the library. Our future work will focus on the next phase of requirements engineering, which is requirements validation.