Plural of duplex; buildings divided into two separate living units, or communication systems with two-way capability.
From duplex (double or twofold, from Latin duplex) plus the plural suffix -es. Used as both a noun for residential buildings and for communication systems.
The 'duplex apartment' became popular in 20th-century cities as a way to house more people—one building doing two jobs, which is exactly what the word duplex means.
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