1. a. Affording unobstructed entrance and exit; not shut or closed. b. Affording unobstructed passage or view: open waters; the open countryside.

2. a. Having no protecting or concealing cover: an open wound; an open sports car. b. Completely obvious; blatant: open disregard of the law. c. Carried on in full view: open warfare; open family strife.

3. a. Not sealed or tied: an open package. b. Spread out; unfolded: an open book.

4. Having interspersed gaps, spaces, or intervals: open ranks; an open weave.

5. a. Accessible to all; unrestricted as to participants: an open competition. b. Free from limitations, boundaries, or restrictions: open registration. c. Enterable by registered voters regardless of political affiliation: an open primary.

6. a. Lacking effective regulation: an open town in which gambling predominated. b. Not legally repressed: open drug trafficking.

7. a. Susceptible; vulnerable: open to interpretation; an issue that is open to question. b. Willing to consider or deal with: open to suggestions.

8. a. Available; obtainable: The job is still open. b. 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. a. Characterized by lack of pretense or reserve; candid: Please be open with me. See synonyms at frank1. b. Free of prejudice; receptive to new ideas and arguments: She listened to the proposal with an open mind. c. Generous: He is very open with his time.

13. Printing. a. Widely spaced or leaded. Used of typeset or other printed matter. b. Having constituent elements separated by a space in writing or printing: The word sea gull is an open compound.

14. Music. a. Not stopped by a finger. Used of a string or hole of an instrument. b. Produced by an unstopped string or hole or without the use of slides, valves, or keys: an open note on a trumpet. c. Played without a mute: an open wind instrument.

15. a. Articulated with the tongue in a low position, as the vowel in far. b. 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. See Regional Note at fair1.

19. Electricity. Containing a gap across which electricity cannot pass.

20. Mathematics. a. Of or relating to an interval containing neither of its endpoints. b. Of, relating to, or being a set such that at least one neighborhood of every point in the set is within the set. c. Of, relating to, or being a set that is the complement of a closed set.

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. To form spaces or gaps between: soldiers opening ranks.

5. a. To remove the cover, cork, or lid from. b. To remove the wrapping from; undo.

6. To unfold so that the inner parts are displayed; spread out: open a newspaper.

7. a. To get (something) going; initiate: open a campaign. b. 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.

10. To make more responsive or understanding.

11. To reveal the secrets of; bare.

12. Law. To recall (an order or a judgment) for a reexamination of its merits.

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. a. To begin; commence: The meeting opened with a call to order. b. To begin business or operation.

7. To give the first public performance: The play opens next week.

8. Games. To make a bid, bet, or lead in starting a game of cards.

9. To give access: The room opens onto a terrace.

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. Sports & Games. A tournament or contest in which both professional and amateur players may participate.

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

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

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

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

5. To make available or accessible: open up new markets.

6. Informal. To accelerate. Used of a motor vehicle.

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