English-Japanese Union Dictionary is a free Chrome add-on developed by hirarin. It combines the WordNet and Wiktionary dictionaries to provide a comprehensive English-Japanese dictionary.

With this add-on, users can easily look up the meanings of English words by selecting them on any webpage. The results are displayed in a convenient pop-up window. Similarly, selecting a Japanese word will display its corresponding English translations. This makes it a versatile tool that can be used as both an English-Japanese and Japanese-English dictionary.

Additionally, users can perform dictionary searches using the browser action located next to the address bar. This allows for quick and easy access to the dictionary functionality. Furthermore, users can star the displayed results to save words for later review and revision.

English-Japanese Union Dictionary is a valuable tool for anyone looking to enhance their English or Japanese language skills while browsing the web.