maiden aunt
From Longman Dictionary of Contemporary EnglishRelated topics: Familymaiden auntˌmaiden ˈaunt noun [countable] old-fashioned SSFan aunt who has never marriedExamples from the Corpusmaiden aunt• When he was eighteen months old, the family broke up, his care passing to a maiden aunt.• Your aupair may be a born maiden aunt.• The man of letters and the maiden aunt.• The maiden aunt who was invited to Walsingham House arrived in a four-wheeler.