Throughout my life I’ve misunderstood a word here and there, even in English. One I remember was “enroach”, which my buddy corrected with an incredulous expression to “encroach”.
One that I have always thought meant “earnest”, “sincere”, was “erstwhile”. But recently I’ve been reading a lot of John McWhorter and he uses the word a lot and it began not to make sense, so I looked it up. Oh lord, it means former or past. So how did I get earnest out of it?
Tonight I heard Chris Matthews talking about the “erstwhile front runners for the POTUS” and it hit me: I had heard it not as a time reference but as a descriptive adjective. And that is how children make errors in their acquisition of the language. David Lightfoot is discussing this in The Development of Language. I have thought for some time that language change internally comes from the desire to emphasize and intensify, but children’s errors can play a role, too.
Thinking about erstwhile after I looked it up, I saw “erst” is the German word “erst”, meaning “first”.
Also, the similarity in spelling between earnest and erstwhile may have played a role.