Analyze how the clue breaks down into definition and wordplay
Break down the clue into definition and wordplay parts
Answer: NOVA | Wordplay: 20ac retired fading star (4)Reverse of AVON (river); this could equally well clue AVON. I was unhappy with “fading” as a description, but a nova is ‘a bright, apparently “new” star (hence the name) that slowly fades over weeks or months