Dual Dictionary

WordNet 3.1 not loaded
Simple English Wiktionary not loaded

Loading the default dictionaries…

One-time download, stored in the app, fully offline afterwards.

A study & research dictionary, right in your browser

About this app — features & terms of use

Dual Dictionary is an offline-first web app built for personal study and research: it looks up English words in parallel panels, with support for your own .mdx/.mdd dictionary files. Everything runs in your browser — data stays on your device, no account, no tracking, no ads.

This app is provided for personal study and research purposes only. It is not a commercial product and is not intended for commercial use or redistribution of any dictionary content. The bundled open data remains available under its own licenses (see NOTICE.md) — this term applies to this deployment only.

  • Parallel lookup: one search, two dictionary views side by side.
  • Open by default: the public edition ships with open-licensed dictionaries (WordNet 3.1, Simple English Dictionary) — free for everyone, no login.
  • Bring your own dictionaries: load any .mdx / .mdd file (MDX format) you own, e.g. learner's dictionaries, into either panel — only files you are authorized to use.
  • Learn-oriented tools: word suggestions, search history, and a built-in spaced-repetition vocabulary list.
  • Install like an app: Add to Home Screen on iOS/Android — works fully offline after that.

Dictionaries & licenses

The public edition ships only open-licensed data (see NOTICE.md):

  • WordNet 3.1 — Princeton University, WordNet 3.1 license (embeds IPA from CMUdict and from Simple English Wiktionary — see NOTICE.md).
  • Simple English Dictionary — derived from Simple English Wiktionary, CC BY-SA 3.0+/4.0 & GFDL.
  • Pronunciations — CMUdict (public domain / BSD, cmusphinx).

Commercial dictionaries (e.g. OALD, LDOCE) are never bundled here; load your own files via ⚙ Advanced only if you are authorized to use them.

How to use

  1. Wait for the first download — the dictionaries are fetched once, then stored in the app and work offline. Progress, speed and time remaining are shown in each panel header; you can cancel or retry from the start screen.
  2. Type a word (e.g. apple) and press Enter — both dictionaries show results side by side.
  3. Save words with ☆ next to the search box, then review them later from ★ in the top bar (built-in spaced repetition).
More features & details
  1. Purpose: this app is a personal study & research tool — non-commercial, no account, no tracking. All dictionary data stays on your own device.
  2. Hear it: tap 🔊 next to the search box to hear the word read aloud using your browser's built-in text-to-speech.
  3. Bring your own dictionary file: open ⚙ Advanced in the top bar to load a .mdx/.mdd dictionary file you have the rights to use into either slot. The public edition ships with open-licensed dictionaries (WordNet 3.1, Simple English) by default — load commercial dictionaries such as OALD/LDOCE only if you own them. See the detailed guide + troubleshooting.
  4. Install on your phone:
    • iPhone / iPad (Safari): Share → Add to Home Screen.
    • Android (Chrome): menu ⋮ → Add to Home screen / Install app.
    Requires iOS 16.4+ (technical requirement: DecompressionStream).
  5. Deploy this app yourself: drag the folder onto Netlify Drop (free) or GitHub Pages. Publishing the app with only its open-licensed bundled data (WordNet 3.1, Simple English Wiktionary) is fine. ⚠️ If you or your group load commercial dictionary files (e.g. OALD/LDOCE), keep that deployment private — serving licensed content as a public service would be redistribution.
  6. Keyboard (desktop): ↑/↓ to pick a suggestion, Enter to search, Esc to hide.
Licenses & terms of use

This app is provided for personal study and research purposes only — non-commercial use. Dictionary files you load remain the property of their respective publishers (e.g. Oxford University Press, Pearson): use only files you are authorized to use, keep them on your own device, and do not redistribute them or serve them publicly.
Spoken audio uses your browser's built-in text-to-speech (no audio files bundled).

Advanced

Optional — most users never need this screen. The app downloads and updates the default dictionaries by itself. Only use this if you want to load your own .mdx/.mdd file into a slot; only load files you have the rights to use — see the terms of use in the Help dialog.

Slot 1 — WordNet 3.1 by default

Slot 2 — Simple English Wiktionary by default

Loading a new .mdx replaces the one currently in that slot. See the detailed loading guide + troubleshooting for supported formats and common errors.

Saved words