Abstract: We present the large-scale linguistic ontology OENT aimed for the using in NLP for the solving of information retrieval tasks such as categorization and query expansion in the domain of natural science and technology. OENT is based on three approaches - traditions of librarian information retrieval thesauri, formal ontologies, WordNet-like resources.Also we describe several additional rules for concepts, text entries and relations. OENT includes 50 thousands concepts, more than 150 thousands text entries, 200 thousands direct relations and more than two millions inherited relations.