100,000 expressions & idioms Understand any expression you come across: from corporate jargon like 💬 touch base or ↩️ circle back to everyday expressions such as 🌊 out of the blue or 🦆 lame duck, as well as idioms like 🍲 spill the beans and 🐎 hold your horses.

40,000 images When you search for a concrete noun or object, images help you grasp the meaning at a glance. Try searching for 🧵 puppytooth, 🎠 merry-go-round, ⚜️ fleur-de-lys, or 💤 bunk bed.

Informal language & slang Everyday conversations are packed with informal expressions and slang. Meanings are clearly tagged, so you'll always know when a word is casual. Look up hangry (😋 hungry + 😡 angry), 😎 rizz, 🕹️ noob, or 🔑 low-key.

Abbreviations & acronyms Quickly decode modern abbreviations and acronyms. Go from IDK to OMG in seconds and stay up to date with popular abbreviations such as 🐐 GOAT, 📜 tl;dr, 👀 POV, or 🖥️ AFK.

Regional usage (US / UK) Reverso highlights regional differences between American and British English. You’ll never have to wonder where a word is commonly used: try lift vs. elevator, courgette vs. zucchini, or popular British slang like dodgy or banter. What’s more, when you search for 'color', you’ll immediately see its British counterpart, 'colour'.

Get more than a simple definition

Translations for each meaning View translations alongside each meaning to see how a word is translated in each context. Simply toggle translations ON and choose among 25+ languages. You can also display the translation of definitions or examples into your native language to deepen your understanding.

Synonyms & related words by meaning View synonyms and related words for each meaning, not just for the word as a whole. This helps you choose the most accurate word for your context. Click the

icon to discover related terms: analogies, antonyms, common collocates, words with same roots, umbrella terms… Try with happening or hunch.

Multiple examples for every meaning Each meaning comes with three real-life examples to show you how the word is used in different contexts. Click the

icon next to the first example to see two additional options and learn to use new vocabulary naturally.

Go from understanding to mastery

Save words for later review Click the

icon to save words you want to revisit. You can also save a specific meaning by clicking on the

icon next to it. For example, you might want to save the word “table” as a verb, which means “to postpone”.

Practice with personalized flashcards Reverso automatically transforms your searches and saved words into personalized flashcards and quizzes, featuring high-quality audio and usage examples. This helps you transform terms you only recognize into words you actually use confidently.

Learn with Netflix, YouTube, and your favorite texts With Reverso Chrome extension, transform movies, TV shows, articles, or song lyrics into an interactive lesson. Look up words and expressions in one click on any website and learn with your favorite content.

Definition of CD4 - Reverso English Dictionary

Acronym

Terms related to CD4

View all translations of CD4

Discover how Reverso redefines the dictionary

Go beyond “simple words”

Get more than a simple definition

Go from understanding to mastery