Google Translate experiments with displaying definitions for the words you're translating. Jérémy Heleine noticed the new feature, which shows a list of definitions, synonyms, examples and related words and snippets. Google also suggests a related translation ("see also").
Definitions and synonyms are also displayed in Google Search, but they're useful in Google Translate too. In addition to using Google Translate as a dictionary, you could improve your translation by picking a better synonym, a context or a more appropriate expression. For example, instead of using "Hello", you could translate "Hi" or "Howdy" and you'll get different translations.
Google Search even lets you translate words when searching for definitions. Search for [define hello], expand the dictionary card and you'll see a section called "translation hello to". Another option is to search for [translate hello into french].
{ Thanks, Frédéric Pereira. }