There are multiple ontology matching approaches that use domain-specific background knowledge to match labels in domain ontologies or classifications. However, they tend to rely on lexical knowledge and do not consider the specificities of domain grammar. In this paper, we demonstrate the usefulness of both lexical and grammatical linguistic domain knowledge for ontology matching through examples from multiple domains. We also provide an evaluation of the impact of such knowledge on a real-world problem of matching classifications of mental illnesses from the health domain. Our experimentation with two matcher tools that use very different matching mechanisms - LogMap and SMATCH - shows that both lexical and grammatical knowledge improve matching results.