Searching and navigation in legal information databases are well studied tasks and highly relevant for practitioners and scientists. Modern legal information databases are the fundament of digital information retrieval, which becomes more and more relevant due to the fact that the amount of information increases continuously and rapidly. This paper investigates how the search and navigation process can be supported by the usage of lexical knowledge such as WordNet or GermaNet. Beside the lexical information of a language, those databases contain information about the linguistic relationships between words, e.g. hyponym and hypernym. An approach is proposed here about how these linguistic relationships can be used to support search and navigation in legal information databases. Analysis of the search term and proposing related hypernyms and hyponyms in the front-end enables users to expand or refine their search term depending on the selected word in the facet. From a legal science point of view, the suggestion of hypernyms or hyponyms has analogies to the well studied grammatical subsumption. The drawbacks, limitations and open issues regarding this approach are discussed at the end of this paper.