Plural of “annex”

The plural of annex is annexes.

Why

"Annex" comes from Latin "annexus," the past participle of "annectere," to bind or attach to something. Unlike many Latin borrowings that kept a Latin plural pattern, "annex" entered English mainly as a verb first (meaning to attach territory or a building to a larger whole), with the noun sense — a building attached to a main one — developing later in English itself. Because it was effectively naturalized as an English word rather than imported wholesale as scholarly vocabulary, it takes the ordinary English -es ending for its sibilant -x rather than any Latin plural form.

There is no competing Latinate plural for "annex" the way there is for words like "vortex" or "apex" — you will not find "annexes" written as "annices" anywhere in reputable usage, because the noun's history in English runs through general building and property vocabulary rather than through science, law, or classical scholarship, the paths that tend to preserve Latin plural endings.

Usage note

"Annexes" is used both for physical buildings (a hospital annex, a library annex) and, less commonly, for attached documents or sections added to a larger text, such as a treaty's annexes. Both senses take the same plural.

Note the stress shift between the noun and the verb: the noun is stressed on the first syllable (AN-eks), while the verb "to annex" (meaning to seize or incorporate territory) is stressed on the second (an-EKS). The plural noun "annexes" keeps the noun's first-syllable stress. Compare this to "codex" or "vortex," both of which stayed rooted in classical scholarship long enough to keep a genuine Latin plural alive in specialist use — "annex" never had that path available to it, since its noun sense developed within English itself, centuries after Latin had stopped being the language new English nouns were coined through.

Common real mistakes

Writers occasionally confuse "annex" the building with "annexation," the political act — they're related but distinct nouns, and only "annex" pluralizes as "annexes"; "annexation" pluralizes regularly as "annexations" when referring to multiple separate acts of annexing territory.

The wider pattern

Among the Latin -ex nouns in English, "annex" sits at the far "fully anglicized" end of the spectrum, alongside words like "complex," where the Latin origin is real but no Latin plural ever gained traction in English usage — contrast this with "vortex" or "codex," where an alternate Latinate plural remains genuinely current. In international law specifically, "annex" describes an attached document forming part of a treaty, and multilateral agreements often contain several such annexes covering technical details separate from the main text — legal drafters rely on precise cross-references between the main body and its annexes, making correct terminology genuinely important in that field.

Examples

• The museum built two annexes to house its growing collection.
• Both annexes were connected to the main building by a covered walkway.
• The hospital's annexes handle outpatient care separate from the main wards.
• Several annexes were added to the treaty after years of negotiation.
• The school's annexes house the science labs and art studios.
• City records list three annexes constructed onto the old courthouse.
• The library's two annexes store archival material not kept on the main shelves.
• New annexes were proposed to relieve overcrowding at the prison.
• The report's annexes contain the raw data behind its conclusions.
• Each annex was built during a different decade of expansion.
• The zoning board approved plans for two more annexes downtown.
• Records show the annexes were added in three separate construction phases.
• The convention center's annexes host smaller meetings during larger events.
• Both annexes required extensive plumbing work before they could open.
• The trade agreement's annexes ran longer than the treaty itself.
• Lawyers cross-referenced each clause against the relevant annexes.
• The new wing added two annexes to the growing research campus.
• Both annexes to the report detailed methodology the main text only summarized.