noun (n)

• a swinging or sliding barrier that will close the entrance to a room or building or vehicle(noun.artifact)

  Example:
  He knocked on the door.
  He slammed the door as he left.
  

  source: wordnet30
• the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close(noun.artifact)

  Example:
  He stuck his head in the doorway.
  

  Synonym:
  doorway, room access, threshold
  

  source: wordnet30
• anything providing a means of access (or escape)(noun.attribute)

  Example:
  We closed the door to Haitian immigrants.
  Education is the door to success.
  

  source: wordnet30
• a structure where people live or work (usually ordered along a street or road)(noun.artifact)

  Example:
  The office next door.
  They live two doors up the street from us.
  

  source: wordnet30
• a room that is entered via a door(noun.artifact)

  Example:
  His office is the third door down the hall on the left.
  

  source: wordnet30
• An opening in the wall of a house or of an apartment, by which to go in and out; an entrance way.(noun)

  source: webster1913