Hi Vic. The phrase 'well-a-day' features in some of our earliest songs dating back to Tudor times and probably earlier. Check out the earliest versions of 'Adieu, Adieu' and 'Devol the Highwayman'. Also one of the earliest forms of the Jack Hall/Benbow tune/format from the 16th century uses it. I interpret it as a verbalised sigh, but it may have had different connotations at different times.