next-door

/N EH1 K S T D AO1 R/
adverb
  1. 1

    In an adjacent building, room or place.

adjective
  1. 1

    That occupies an adjacent place, especially the building immediately to the left or right.

Source: https://en.wiktionary.org/wiki/next%20door, https://en.wiktionary.org/wiki/next-door