Awesome Dictionary от ramblingThinker

Awesome Dictionary gives fast, in-context word definitions on any webpage.

How it works:

Double-click a word to open an inline definition bubble.
Right-click selected text and choose Define '%s'.
Search words directly from the toolbar popup.
Features:

Clean, readable definition layout with part of speech and examples.
Recent lookup history stored locally for quick re-use.
Configurable settings for bubble timeout, auto-close behavior, context menu toggle, and history size.
Offline resilience: when the dictionary API is temporarily unavailable, previously cached definitions can be shown.
Privacy and data use:

No account required.
No analytics, tracking, or advertising.
The add-on only sends the queried word to https://api.dictionaryapi.dev to fetch a definition.
Settings, history, and cached definitions are stored locally in browser extension storage.