The dictionary's primary purpose was to teach missionaries spoken Japanese. As needed, the authors identify such things as regional dialect, written and spoken forms, women's and children's language, elegant and vulgar words, and Buddhist vocabulary. Many of these words had never been written in any known text before the "Nippo Jisho" was published. The system of romanization used by the "Nippo Jisho" also reflects the phonetics of 16th-century Japanese (Late Middle Japanese), which is not identical to modern Japanese. Both these points provide present-day linguists valuable insight into the Japanese language of the Sengoku period of Japanese history and how it has evolved into its modern form. The dictionary also yields information on rhyming words, individual pronunciation, meaning, usage, names of plants and animals, popular phrases, and customs of the times.