This is a double definition - the clue gives two different ways to describe the same answer, one in English and one involving the Italian phrase.
The Italian phrase 'Zuppa inglese' translates to a specific English dessert name. The word 'niente' means 'nothing' in Italian, and you need something that means 'not nothing' - though perhaps only just barely something.
Answer: TRIFLE | 'Zuppa inglese' is the Italian name for trifle (literally 'English soup'). A trifle is 'not nothing' (non è niente) - though perhaps nearly so, being considered something small or insignificant.