Double-click any word.Even inside PDFs.
QuickDef is a Chrome extension that provides instant, AI-powered word definitions without leaving the page you're reading. Double-click any word — on any webpage or PDF — and a definition appears in a popup overlay. You can also drag across a whole phrase, up to seven words, and QuickDef explains what it means together rather than word by word — so phrasal verbs like “put up with” and idioms like “a piece of cake” get a real explanation instead of definitions of their separate words. For English language learners, it generates context-aware explanations in plain English calibrated to A2–B1 CEFR level, based on the sentence the word appeared in. A traditional dictionary mode is also available, with phonetics and audio pronunciation.
Get the meaning it has in that sentence — in plain English, in a popup, without leaving the page. Works on PDFs and academic papers, where Google Dictionary doesn't.
Free forever: 10 AI definitions per day and up to 25 saved words, plus unlimited traditional dictionary lookups. No credit card, no signup.
Last updated: August 2026
Why English Learners Struggle
Existing tools create more problems than they solve for language learners.
Google Dictionary Doesn't Work on PDFs
Browser extensions fail when you're reading research papers, ebooks, or documents in PDF format.
Definitions Are Too Complex for Learners
Traditional dictionaries use advanced vocabulary to explain words, making it harder for non-native speakers.
Switching Tabs Breaks Your Reading Flow
Opening a new tab, typing the word, reading the definition, then returning kills your concentration.
No Easy Way to Save and Review Words
You look up the same words repeatedly because there's no system to track and study what you've learned.
How QuickDef Fixes It
A simple tool built around one goal: understand any word, keep reading.
Watch DemoWorks Where Others Fail
Web pages, PDFs — even academic papers. Google Dictionary breaks on PDFs. QuickDef doesn’t.
Learner-First Explanations
AI explains words in plain English, based on how the word is used in that sentence — not dictionary jargon.
Words & Phrases, Without Leaving the Page
Double-click a word. Drag across a phrase like “put up with” and get the meaning of the whole expression — no tabs, no copy-paste.
Save Words While You Read
One click to save words with their meaning and sentence. Review later with simple flashcards.
Your Words, Your Data
Export anytime. No lock-in. No tricks.
Free to Start
Use it immediately. Upgrade only when you actually need more.
Common Questions
Everything you need to know about QuickDef.
What is QuickDef?
QuickDef is a Chrome extension that provides instant, AI-powered definitions without leaving the page you're reading. Double-click any word — on any webpage or PDF — and a definition appears in a small popup overlay. You can also drag across a phrase and get the meaning of the whole expression.
How do I look up the meaning of a phrase or idiom?
Drag across the phrase — up to seven words — and a small “Define” button appears next to your selection. Click it and QuickDef explains what the phrase means as a whole. Selecting text without clicking Define never triggers a lookup, so copying text works normally.
Why can't a normal dictionary explain phrasal verbs?
Because the meaning isn't the sum of the words. “Put up with” has nothing to do with putting, up, or with — it means to tolerate something. A dictionary looks up one word at a time, so it can only give you the parts and leave you to guess. QuickDef sends the whole phrase to an AI with the sentence it appeared in.
Does QuickDef work on PDFs?
Yes. QuickDef works on PDFs and academic papers, where most dictionary extensions fail. Double-click any word in a PDF — or drag across a phrase — and get an instant definition in a popup, without switching tabs or copying text elsewhere.
What's the difference between Simple mode and Full mode?
Simple mode uses AI (GPT-4o-mini) to generate a plain-language definition based on sentence context. Full mode pulls traditional dictionary definitions from the Free Dictionary API, including phonetic transcription and audio pronunciation.
Who is QuickDef designed for?
QuickDef is designed for English language learners (ELLs), students reading academic content, and professionals working in English as a second language. Definitions are calibrated to A2–B1 CEFR level.
How much does QuickDef cost?
Free tier includes 10 AI definitions per day and up to 25 saved words — dictionary mode is always unlimited. Premium is ~$4/month or ~$30/year (~$2.50/month), billed in USD via card or in IDR via Xendit.
How does the AI definition work?
When you double-click a word — or select a phrase — QuickDef sends it along with the surrounding sentence to GPT-4o-mini. The AI returns a definition that matches how it is being used in that specific sentence, not a generic dictionary entry.
Does QuickDef save words for later review?
Yes. QuickDef saves words along with the sentence they appeared in. Free accounts save up to 25 words; Premium accounts have unlimited saving. Saved words sync across devices.
Do I need to create an account?
No. QuickDef supports anonymous sign-in — your first use automatically creates a private account with no email or password required. Full sign-up is available if you want persistent, named access.
Which browsers does QuickDef work in?
QuickDef works in Chrome and all Chromium-based browsers (Brave, Edge, Opera, Arc). Firefox and Safari are not currently supported.
What is the best Chrome extension for looking up word definitions?
QuickDef lets you double-click any word — or drag across a phrase — for an instant AI-powered definition without leaving the page. It works on PDFs, academic papers, and any webpage, with context-aware explanations based on how the word or phrase is actually used.