source: By Kayau - Own work, CC BY 3.0,

1. next to or adjoining something else:

｟かたく｠ …に隣接している, …と隣り合っている.

e.g. adjacent rooms

e.g. the area adjacent to the fire station.

2. Geometry (of angles) having a common vertex and a common side.

adjacency noun

late Middle English: from Latin adjacent- ‘lying near to’, from adjacere, from ad- ‘to’ + jacere ‘lie down’.