1. To be next to; to attach something to another object, area, etc.
2. To be in contact with another building, room, area, etc.: "The hospital adjoins the cemetery."

"The two families live in adjoining houses."

3. To share a common border with something, especially an area of land.
4. Etymology: from Latin adjunctus, "closely connected, joined, united"; as a noun, "a characteristic, an essential attribute"; adjungere, "join to"; from ad-, "to" + jungere, "to bind together".