What is erstwhile?

Erstwhile is an adjective that means former or previous. It is often used to describe something that existed or happened in the past but no longer does. For example, erstwhile friends are people who used to be friends but no longer are. Another example would be an erstwhile factory that used to produce goods but has since closed down. The word originated from the Old English word 'aerest' which means 'first' and 'hwil' which means 'while' or 'time'.