We present Reverso Define, an innovative English dictionary designed to support translation professionals with AI-powered, context-aware definitions. Built using a hybrid approach combining Large Language Models and expert linguists, it offers precise definitions with special attention to multi-word expressions and domain-specific terminology. The system provides comprehensive coverage of technical domains relevant to professional translators while maintaining daily updates to address emerging terminology needs. It also provides indicative translations in 26 languages linked to each meaning, and variants within languages, when appropriate, and has links to Reverso Context, the range of contextual and corpus-based bilingual dictionaries, and Reverso Synonyms. We will show the various ways to use it with concrete examples and give some insights on its design and creation process.