Attach

Annex is the abbreviated word for annexation, which means to attach, adjoin or affix a physical structure to something larger.

Annexed Building

Derived from the "attach" definition, a subsidiary building or an addition to a building is often given the proper name of Annex, indicating that it is a later addition to an already substantial structure.

Incorporation

Another variation of annexation is when a city or state incorporates a smaller region into its larger territory. This does not refer to the unofficial process of urban sprawl or metropolitan statistical areas but rather when a conscious effort is made, as when Germany annexed Austria under the Third Reich.

Affix

When a seal or signature is added to a document, such as an appendix, this is deemed an annexation. Likewise, when a book or composition is added to (with written material), it is also deemed an annexation.

To Take

When something is taken without permission, it has been annexed.

Consequences/Condition

When something is added as a condition, or added as a consequence of something else, it has been annexed. For example, "certain privileges were annexed to the prisoners after good behavior."

Source:

Dictionary.com

Oxford English Dictionary