The Collaborative International Dictionary of English v.0.48:

Door \Door\, n. [OE. dore, dure, AS. duru; akin to OS. dura,
   dor, D. deur, OHG. turi, door, tor gate, G. th["u]r, thor,
   Icel. dyrr, Dan. d["o]r, Sw. d["o]rr, Goth. daur, Lith.
   durys, Russ. dvere, Olr. dorus, L. fores, Gr. ?; cf. Skr.
   dur, dv[=a]ra. [root]246. Cf. Foreign.]
   1. An opening in the wall of a house or of an apartment, by
      which to go in and out; an entrance way.
      [1913 Webster]

            To the same end, men several paths may tread,
            As many doors into one temple lead.   --Denham.
      [1913 Webster]

   2. The frame or barrier of boards, or other material, usually
      turning on hinges, by which an entrance way into a house
      or apartment is closed and opened.
      [1913 Webster]

            At last he came unto an iron door
            That fast was locked.                 --Spenser.
      [1913 Webster]

   3. Passage; means of approach or access.
      [1913 Webster]

            I am the door; by me if any man enter in, he shall
            be saved.                             --John x. 9.
      [1913 Webster]

   4. An entrance way, but taken in the sense of the house or
      apartment to which it leads.
      [1913 Webster]

            Martin's office is now the second door in the
            street.                               --Arbuthnot.
      [1913 Webster]

   Blank door, Blind door, etc. (Arch.) See under Blank,
      Blind, etc.

   In doors, or Within doors, within the house.

   Next door to, near to; bordering on.
      [1913 Webster]

            A riot unpunished is but next door to a tumult.
                                                  --L'Estrange.


   Out of doors, or Without doors, and, [colloquially], Out
   doors, out of the house; in open air; abroad; away; lost.
      [1913 Webster]

            His imaginary title of fatherhood is out of doors.
                                                  --Locke.

   To lay (a fault, misfortune, etc.) at one's door, to charge
      one with a fault; to blame for.

   To lie at one's door, to be imputable or chargeable to.
      [1913 Webster]

            If I have failed, the fault lies wholly at my door.
                                                  --Dryden.
      [1913 Webster]

   Note: Door is used in an adjectival construction or as the
         first part of a compound (with or without the hyphen),
         as, door frame, doorbell or door bell, door knob or
         doorknob, door latch or doorlatch, door jamb, door
         handle, door mat, door panel.
         [1913 Webster]