The act of attaching, adding, joining, or uniting one thing to another ; generally spoken of the connection of a smaller or subordinate thing with a larger or principal thing. The attaching an illustrative or auxiliary document to a deposi-tion, pleading, deed, etc., is called “annexing” it. So the incorporation of newly-ac-qulred territory Into the national domain, as an integral part thereof, is called “annexation,” as in the case of the addition of Texas to the United States
Source: Black's Law Dictionary 2nd Ed (1910)