adj.
          - allowing access, passage, or view; not closed, fastened, or restricted.
 - exposed to the air or to view or attack; not covered or protected:
 an open boat.
 ▸(of land) not covered with buildings or trees.
 ▸
(open to)
 vulnerable or subject to.
 ▸(of a town or city) officially declared to be undefended, and so immune under international law from bombardment.
 - spread out or unfolded. 
▸(of a book) with the covers parted and able to be read.
 - admitting customers or visitors; available for business. 
▸freely available or accessible.
 ▸(of an offer or opportunity) still available.
 - frank and communicative. 
▸not concealed; manifest.
 ▸welcoming public discussion, criticism, and enquiry:
 open government.
 - (of a matter) not finally settled. 
▸
(often open to)
 receptive to new ideas.
 ▸
(open to)
 admitting of; making possible.
 - Music  (of a string) allowed to vibrate along its whole length. 
▸(of a pipe) unstopped at each end.
 - Phonetics  (of a vowel) produced with a relatively wide opening of the mouth and the tongue kept low. 
▸(of a syllable) ending in a vowel.
 - (of an electric circuit) having a break in the conducting path.
 - (of a fabric) loosely knitted or woven.
 
v.
      - move (a door, window, etc.) so that it is open. 
▸undo or remove the cover or fastening of.
 ▸
(open on to/into)
 (of a door, window, etc.) give access to.
 - unfold or be unfolded; spread out. 
▸part the covers of (a book) to read it.
 ▸(of a prospect) extend into view.
 - make or become open for customers or visitors. 
▸ceremonially declare (a building, road, etc.) to be completed and ready for use.
 - formally begin or establish. 
▸
(open up or open fire)
 begin shooting.
 ▸(of a counsel in a law court) make a preliminary statement in (a case) before calling witnesses.
 ▸Bridge  make (the first bid) in the auction.
 - make available or more widely known. 
▸
(open out/up)
 become more communicative or confiding.
 - break the conducting path of (an electric circuit).
 
n.
   - 
(the open)
 outdoors or in the countryside. 
▸
(usu. in phr. in/into the open)
 a lack of concealment or secrecy.
 - 
(Open)
 a championship or competition with no restrictions on who may compete.
 - an accidental break in the conducting path for an electric current.
 
 
  Phrase
  
    - the open air
 an unenclosed space outdoors.  - in open court
 in a court of law, before the judge and the public.  - open-and-shut
 (of a case or argument) admitting no doubt or dispute; straightforward. 
   
  Derivative
  
    - openable adj.
  - openness n.
 
   
  Etymology
  OE open (adj.), openian (v.), of Gmc origin, from the root of the adv. up.