A (n American) person I follow on Twitter–no names–just used “by-election” to refer to the recent Congressional race in upstate New York.
My work here is done.
A (n American) person I follow on Twitter–no names–just used “by-election” to refer to the recent Congressional race in upstate New York.
My work here is done.
notoneoffbritishisms.com 
Many English place-names end in “by”. Scawby, Selby etc. It means village or farmstead. A by-election therefore simply means a small local election.
To correct the above, I believe that by-election is what Americans refer to as a ‘mid-term’ election.
Actually, it would be more precise to say that it means what Americans call a “special election.” Since American presidents are elected every four years and members of the House every two, a “midterm election” is the regularly scheduled House (and one-third of the Senate, and also many state governors) election held in a presidential off year. A “special election” is one held outside the cycle because of death, resignation, appointment to a different office, etc. by an incumbent.
I think that is correct – in Canada a by-election would correspond to the American special election, and Canada models its political system on the British.
haark’s folk etymology fails under scrutiny. The ‘by-‘ is the standard prefix meaning side or incidental, as in so many other compounds such as by-blow, by catch, by-play, by-product and so on
I thought that until about fifty years ago, when I came across an article about British politics that put me right. (And no, I can’t find it now!) My shorter OED doesn’t mention ‘by election’, but does mention the closely related by, or bye, law as having Scandinavian roots meaning ‘habitation’.
If I can dig up something better I’ll post it.