n. — Politics
an election held between regularly scheduled general elections, to fill a position that has become vacant during the term of office.
Type: 5. Frequency — Common in many English-speaking countries (see Chart 2 for one spelling variant), by-elections have been part of the Canadian political landscape since the 19th century. The form byelection has far greater currency in Canada than elsewhere (see Chart 1). Today, however, by-election is still more widely used than the Canadian innovation byelection.
See also Gage-1, s.v. "by-election", ITP Nelson, s.v. "by-election", and OED-3, s.v. "by-election", W-3, s.v. "by-election", AHD-5, s.v. "by-election".
- The spelling bye-election is prevalent in Ireland (103 Frequency Index points), followed by New Zealand (43 points); Canada has a very low score of not even 7 points (23 Jan. 2016).
Images:

Chart 1: Internet Domain Search, 6 Dec. 2012 
Chart 2: Internet Domain Search, 24 Oct. 2012