Click Define turns every word on the web into a quick lookup. Just double-click, no shortcuts, no menus, no leaving the page. On Firefox for Android, long-press instead. Features

Double-click any word (or long-press on mobile) to open a small popup with its definition.
Hundreds of languages via Wiktionary. When a word has entries in multiple languages, a dropdown lets you pick which one to view. Defaults to the page's language automatically; settable in preferences.
Pronunciation with IPA and an audio button (English).
Synonyms and antonyms as clickable chips - click one to look it up; a back button returns to the previous word.
Inflected-form awareness - for entries that just point elsewhere ("plural of box", "simple past of run", "misspelling of receive"), a chip in the header jumps you to the base word. Optional setting to make this automatic.
Lemma fallback so inflected forms without their own entry still resolve (e.g. "happily" → "happy").
Sticky popup that scrolls with the word being defined.
Network resilience - retries transient errors silently and shows a clear retry button when something really fails.
Light and dark mode matched to your system theme.
Privacy-first - only the word you double-click is sent to public dictionary APIs. Page content, browsing history, and personal data are never collected or transmitted.

How it works When you double-click a word, Click Define queries Wiktionary for multilingual definitions, the Free Dictionary API for English pronunciation and audio, and Datamuse for synonyms/antonyms. No accounts, no API keys, no tracking. Press Esc or click outside the popup to dismiss it.

HalfToast

Published Firefox add-on:

Click Define