Meaning

noun an addition that extends a main building

verb take (territory) as if by conquest

verb attach to

originFrom Middle English annexen, anexen, from Old French annexer (“to join”), from Medieval Latin annexāre, infinitive of annexō, frequentative of Latin annectō (“bind to”), from ad (“to”) + nectō (“tie, bind”). Compare the rare annect. Doublet of adnex.

Etymology from Wiktionary, CC BY-SA 3.0