Indicates a shift in time to express that someone or something was, but is no longer, in a specific role or state. His erstwhile mentor retired last spring.
Pro Tip 2/3
Emotional Distance
Implies a psychological or emotional separation from something or someone in the past. She returned to her erstwhile home, feeling like a stranger.
Pro Tip 3/3
Narrative Change
Useful in storytelling to introduce a change in a character's life or situation. The erstwhile villain redeemed himself in the story's climax.