n. & adj. — Housing
a building separated into four residences; fourplex.
Type: 5. Frequency — The original meaning of quadruplex was "fourfold". There are numerous other meanings, some of them older, such as Thomas Edison's quadruplex telegraph system, and the modern quadriplex baseball field layout. The meaning referring to houses has a history dating back to around WWI. Other, related forms, such as duplex and triplex, fourplex and fiveplex, are much younger (contrary to the etymology offered in COD-2, which gives duplex as the source for quadriplex). Quadruplex appears to be most frequent in Canada (see Chart 1).
See also COD-2, s.v. "quadruplex", which is marked "Cdn", and OED-3, s.v. "quadruplex" (2), which is marked "orig. and chiefly N. Amer.".
See also: duplex (def. 1) fiveplex fourplex triplex
- 1919  There is a unique feature of the quadruplex houses. They will, of course, have no rear yards, all the lawn being at the front and side. 
- 1920  Discuss Kindergarten For Quadruplex Houses The establishment of a kindergarten school at the north end [...] in connection with quadruplex housing block planned for northwest corner of Rockwell and Prescott avenues was discussed yesterday at the meeting of the committee. 
- 1930  Each Quadruplex building has: Over-sized Hot Water Furnaces 
- 1936  If the federal government accepts the relief housing scheme, as submitted recently by a special committee, 1,900 homes, built along the lines of the quadruplex and duplex types pictures here, will be erected in suburban municipalities surrounding Toronto, to house relief families. 
- 1947  Eastern Beach district, 4-family quadruplex, near the lake on Scarboro Beach, each apartment is modernly laid out with 5 rooms, oak floors, chestnut trim. 
- 1952  QUADRUPLEX SUMMERHILL GARDENS 35,000 - Brick, oil heated 4-plex in excellent rental area near all services. 
- 1985  The petition says some tenants of a quadruplex on the street allow their cats to run loose. 
- 2008  The resort's 10 widely spaced duplex bungalows and four quadruplex villas are only steps from a magnificent six-kilometre sweep of coral-sand beach. 
- 2016  Montreal's arson squad was investigating two incidents that occurred in the early hours of Monday.
The first was a fire in a quadruplex that police believe was criminally set around 1 a.m. in the Pierrefonds-Roxboro borough. 
Images:
Chart 1: Internet Domain Search, 18 Jun. 2013