The definition of annex means to attach something, particularly to a larger entity.(verb)
An example of annex is to acquire new states into a country.
Annex is defined as an additional part of a building or a nearby building which is used as part of the main building.(noun)
An example of an annex is a building in the parking lot which is used as additional office space to supplement the office space in the main building.
See annex in Webster's New World College Dictionary
Origin: ME annexen < OFr annexer < L annexus, pp. of annectere < ad-, to + nectere, to tie, bind: see net
See annex in American Heritage Dictionary 4
transitive verb an·nexed, an·nex·ing, an·nex·es
Origin: Middle English annexen
Origin: , from Old French annexer
Origin: , from Latin annectere, annex-, to connect
Origin: : ad-, ad-
Origin: + nectere, to bind; see ned- in Indo-European roots.
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