next door

Short definition from Wiktionary

Adverb

1. 1
   In an adjacent building, room or place.
2. 2
   Alternative spelling of next door.

Adjective

1. 1
   That is in an adjacent place; that is located next door.
2. 2
   that occupies an adjacent place, especially the building immediately to the left or right

Preposition

1. 1
   Next door to.