(1) Near, neighboring. (2) Sharing a common boundary or border.
Example:
The warehouse was adjacent to the junction of the two raging rivers, so the body could have been quickly disposed of.
Adjacent contains the prefix ad-, "near or toward," so what is adjacent lies near its neighbor. In the former Yugoslavia, the Serbs and Croats have seized adjacent land from the Bosnians. Anyone buying a house is naturally curious about who lives on the adjacent lots. In geometry we speak of adjacent sides and angles. Though in each of these cases adjacent means "touching," it may also mean simply "neighboring" or "nearby."