n. — Housing
an abbreviation for semi-detached house, a house that shares a wall with one other house; a duplex.
Semi is prevalent in Irish English, and British attestations of the term date back to the early 20th century (see OED-3, s.v. "semi" [1]), which lists a first attestation (to date) from 1912 in the UK. Semi continues to have currency in Ireland, where it is possibly a preservation from UK English. It is comparatively infrequent in Canada and in the United States (see Chart 1), and quotations are difficult to find in Canadian sources.
See also COD-2, s.v. "semi," (1) which is marked "Cdn & Brit."
See also: duplex
- While semi-detached does occur as a term, the dominant Canadian word for this Irish English and UK term is duplex (see Chart 1).
- 1978  For this year, the total starts are forecast at 225,000 units with single family units at around 104,000, semis at 20,000, row units at 29,000 and apartments at 72,000. 
- 1988  Total housing starts, which include singles, semis, condos and duplexes for 1988 were 40,000. This will decline 5 per cent to 38,000 in 1989, he said. 
- 1998  Bargain bonanza best describes the inventory blowout by Richcraft Homes. Singles, towns, semis and terrace homes across the city are being discounted by as much as $10,000. 
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Chart 1: Internet Domain Search, 3 Mar. 2013