Short for semi-trailers or semi-detached houses; trucks with detachable trailers, or pairs of houses sharing one wall.
Shortened form of 'semi-trailer' (from Latin 'semi-' meaning 'half') and 'semi-detached.' Both uses evolved in the 20th century as abbreviations for longer terms.
Semi-truck trailers are called 'semis' because they have wheels on only one end—the front of the trailer sits on the tractor unit, making it partially supported (hence 'semi'). British suburbs are often filled with 'semis'—a uniquely efficient way to house more families!
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