Erstwhile is one of those lovely sounding words that you think should have long since fallen out of use. Fortunetaly it hasn't. It is still alive and well and living in bookland if not often in our conversations.
It means 'former, once, at a previous time or belonging to some prior time". Such as in the phrase 'her erstwhile friend'.
A word with the same meaning is quondam whose usage does seem to have pretty well died out.
Katie aged 6 months
16 hours ago