This appears to be a misspelling or variant spelling; standard spelling is 'bonne' (a French nursemaid or children's nurse).
From French 'bonne' (literally 'good woman'), feminine form of 'bon' (good), used since the 18th century for household servants who cared for children.
Victorian and Edwardian wealthy families prided themselves on hiring French bonnes, making the word a status symbol—having a 'bonne' meant you were cosmopolitan and rich enough for French staff.
Complete word intelligence in one call. Free tier — 50 lookups/day.