* "Fancy" as in "I don't fancy that" (meaning I don't like it): "Je n'aime pas ça"
* "Fancy" as in "a fancy restaurant": "un restaurant chic" or "un restaurant élégant"
* "Fancy" as in "fancy dress": "costume de fête"
So there's no single word for "fancy" in French. It depends on the specific meaning you're trying to convey.