Cybersecurity ontology development is typically carried out by cybersecurity experts and ontology engineers. While some existing works focus on extracting cybersecurity knowledge from either textual or structured data, few address the challenge of handling both types of data simultaneously. This paper presents Locust, a tool integrating structured data and domain corpus for comprehensive cybersecurity ontology generation. We use open source cybersecurity specifications as structured input to build the skeleton of the ontology, and use the domain corpus to enrich and finalise the ontology. Additionally, we propose a methodology for filtering and simplifying the ontology using hierarchical clustering and multi-way tree. Experimental results demonstrate the effectiveness of our approach in acquiring a cybersecurity ontology from specific domain data sources. Locust is implemented in Java and is available as an open source tool.