Dual Dictionary is a free, offline-first English–English dictionary web app. When both sources are available, one search compares WordNet 3.1 with the Simple English Wiktionary. It includes saved words, browser text-to-speech, reader mode with tap-to-lookup, optional English–Vietnamese support, and user-owned .mdx/.mdd files. After dictionary data finishes downloading, it can work offline on the same device.
