This came up earlier today over on the Twitterthing, and it’s worth a short blog post.
There’s “erstwhile” and there’s “ersatz,” and neither one means “so-called.”
I’ve seen it happen enough times that I made a note for myself. A writer wants to use a fancier word instead of “so-called,” and they grab “erstwhile.” Trouble is, that means “formerly” or (currently, more often) “former.” What they think they want is “ersatz,” which means “substitute, replacement, fake, faux” and suchlike that there. It doesn’t mean “so-called.”
The erstwhile mayor showed up at the commemoration wearing an ersatz fur with alarmingly realistic holes as if actual moths had eaten at it.
If you want to say “so-called,” say it. Just like that. It’s legal. I swear.