o·pen·ing (ṓpə-nĭng)

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noun 

1. The act or an instance of becoming open or being made to open.
2. An open space serving as a passage or gap.
3. A breach or aperture.
4. A clearing in the woods.
5. The first part or stage, as of a book.
6. The first performance: the opening of a play.
7. A formal commencement of operation: attended the opening of the new museum.
8. Games A specific pattern or series of beginning moves in certain games, especially chess.
9. An opportunity affording a chance of success. See synonyms at opportunity
10. An unfilled job or position; a vacancy.

o·pen (ṓpən)

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[Middle English, from Old English.]

adjective 

1. 1. Affording unobstructed entrance and exit; not shut or closed.
   2. Affording unobstructed passage or view: open waters; the open countryside.
2. 1. Having no protecting or concealing cover: an open wound; an open sports car.
   2. Completely obvious; blatant: open disregard of the law.
   3. Carried on in full view: open warfare; open family strife.
   4. Sports Not closely defended by an opponent: an open receiver.
3. 1. Not sealed or tied: an open package.
   2. Spread out; unfolded: an open book.
4. Having interspersed gaps, spaces, or intervals: open ranks; an open weave.
5. 1. Accessible to all; unrestricted as to participants: an open competition.
   2. Free from limitations, boundaries, or restrictions: open registration.
   3. Enterable by registered voters regardless of political affiliation: an open primary.
   4. Computer Science Of or relating to a file that can be accessed.
6. 1. Lacking effective regulation: an open town in which gambling predominated.
   2. Not legally repressed: open drug trafficking.
7. 1. Susceptible; vulnerable: open to interpretation; an issue that is open to question.
   2. Willing to consider or deal with something: open to suggestions.
8. 1. Available; obtainable: The job is still open.
   2. Available for use: an open account; the only course open to us.
9. Ready to transact business: The store is open.
10. Not engaged or filled: has an open hour for emergency cases.
11. Not yet decided; subject to further thought: an open question.
12. 1. Characterized by lack of pretense or reserve; candid: Please be open with me. See synonyms at frank¹
    2. Free of prejudice; receptive to new ideas and arguments: She listened to the proposal with an open mind.
    3. Generous: He is very open with his time.
13. Printing
    1. Widely spaced or leaded. Used of typeset or other printed matter.
    2. Having constituent elements separated by a space in writing or printing: The word is an open compound.
14. Music
    1. Not stopped by a finger. Used of a string or hole of an instrument.
    2. Produced by an unstopped string or hole or without the use of slides, valves, or keys: an open note on a trumpet.
    3. Played without a mute: an open wind instrument.
15. Linguistics
    1. Articulated with the tongue in a low position, as the vowel in far.
    2. Ending in a vowel or diphthong: an open syllable.
16. Designating a method of punctuation in which commas and other marks are used sparingly.
17. Being in operation; live: an open microphone.
18. New England Clear. Used of weather.
19. Electricity Containing a gap across which electricity cannot pass: an open circuit.
20. Mathematics
    1. Of or relating to an interval containing neither of its endpoints.
    2. Of or being a set such that at least one neighborhood of every point in the set is within the set.
    3. Of or being a set that is the complement of a closed set.
21. Sports
    1. Having the forward foot farther from the intended point of impact with the ball than the rear foot: an open batting stance.
    2. Held or swung with the top or outer edge of the striking face pointing slightly farther away from the objective than the lower or inner edge: The club struck the ball with an open face, causing a slice.
22. Physics Of or relating to a model of the universe in which there is not sufficient matter to halt its expansion.

verb: o·pened, o·pen·ing, o·pens. 

transitive verb 

1. To release from a closed or fastened position.
2. To remove obstructions from; clear.
3. To make or force an opening in: open an old wound.
4. 1. To form spaces or gaps between: soldiers opening ranks.
   2. To break the continuity of; make a gap in: open a circuit.
5. 1. To remove the cover, cork, or lid from.
   2. To remove the wrapping from; undo.
6. To unfold so that the inner parts are displayed; spread out: open a newspaper.
7. 1. To get (something) going; initiate: open a campaign.
   2. To commence the operation of: open a new business.
8. Games To begin (the action in a game of cards) by making the first bid, placing the first bet, or playing the first lead.
9. To make available for use: opened the area to commercial development; opened the computer file and retrieved some data.
10. To make more responsive or understanding.
11. To reveal the secrets of; bare.
12. Sports To modify (one's stance), as in baseball or golf, so that it is open.
13. Law To recall (an order or judgment) for a reexamination of its merits.

intransitive verb 

1. To become open: The door opened slowly.
2. To draw apart; separate: The wound opened under pressure.
3. To spread apart; unfold.
4. To come into view; become revealed: The plain opened before us.
5. To become receptive or understanding.
6. 1. To begin; commence: The meeting opened with a call to order.
   2. To begin business or operation: The store opens early on Saturday.
7. To be performed, shown, or made available to the public for the first time: The play opens next week.
8. To be priced or listed at a specified amount when trading begins: Shares opened high and fell sharply.
9. Games To make a bid, bet, or lead in starting a game of cards.
10. To give access: The room opens onto a terrace.

noun 

1. An unobstructed area of land or water.
2. The outdoors: camping in the open.
3. An undisguised or unconcealed state: brought the problem out into the open.
4. A tournament or contest in which both professional and amateur players may participate.

phrasal verbs

open up

To spread out; unfold: A green valley opened up before us.

To begin operation: The new store opens up next month. To begin firing: The artillery opened up at dawn.

Informal To speak freely and candidly: At last the frightened witness opened up and told the truth.

To make an opening in by cutting: The surgeon opened up the patient's chest.

To make available or accessible: open up new markets.

Informal To accelerate. Used of a motor vehicle.

idioms

open fire

To begin firing on.

open (one's) eyes

To become aware of the truth of a situation.

derivatives

ópen·ly

adverb

ópen·ness

noun