o·pen / ˈōpən/ • adj. 1. allowing access, passage, or a view through an empty space; not closed or blocked up: it was a warm evening and the window was open the door was wide open. ∎  (of a container) not fastened or sealed; in a position or with the lid or other covering in a position allowing access to the inside part or the contents: the case burst open and its contents flew all over the place. ∎  (of a garment or its fasteners) not buttoned or fastened: his tie was knotted below the open collar of his shirt. ∎  (of the mouth or eyes) with lips or lids parted: his eyes were open but he could see nothing. ∎  free from obstructions: the pass is kept open all year by snowplows. ∎ inf. (of a car or house) unlocked. ∎ Phonet. (of a vowel) produced with a relatively wide opening of the mouth and the tongue kept low. ∎ Phonet. (of a syllable) ending in a vowel. ∎  (of the bowels) not constipated. ∎  (of a game or style of play) characterized by action that is spread out over the field.2. exposed to the air or to view; not covered: an open fire burned in the grate. ∎  (of an area of land) not covered with buildings or trees: increasing numbers of new houses in open countryside. ∎  having spaces or gaps between elements: air circulates more readily through an open tree. ∎  (of a fabric) loosely knitted or woven. ∎  (of a team member in a game) unguarded and therefore able to receive a pass: the trick is spreading the defense so that at least one receiver gets open. ∎  (of a goalmouth or other object of attack in a game) unprotected; vulnerable. ∎  (of a boat) without a deck: days without food and water in an open boat. ∎  (open to) likely to suffer from or be affected by; vulnerable or subject to: the system is open to abuse. ∎  (of a town or city) officially declared to be undefended, and so immune under international law from bombardment. ∎  with the outer edges or sides drawn away from each other; unfolded: the trees had buds and a few open flowers. ∎  (of a book or file) with the covers parted or the contents in view, allowing it to be read: she was copying verses from an open Bible | fig. her mind was an open book to him. ∎  (of a hand) not clenched into a fist. ∎  damaged or injured by a deep cut in the surface: he had his arm slashed open.3. (of a store, place of entertainment, etc.) officially admitting customers or visitors; available for business: the store stays open until 9 p.m. ∎  (of a bank account) available for transactions: the minimum required to keep the account open. ∎  (of a telephone line) ready to take calls: our free advice line is open from 8:30 to 5:30. ∎  (of a choice, offer, or opportunity) still available; such that people can take advantage of it: the offer is open while supplies last we need to consider what options are left open.4. (of a person) frank and communicative; not given to deception or concealment: she was open and naive I was quite open about my views. ∎  not concealed; manifest: his eyes showed open admiration. ∎  (of conflict) fully developed and unconcealed: the dispute erupted into open war. ∎  involving no concealment, restraint, or deception; welcoming discussion, criticism, and inquiry: the conclusions were reached in open discussion.5. (of a question, case, or decision) not finally settled; still admitting of debate: students' choice of major can be kept open until the second year. ∎  (of the mind) accessible to new ideas; unprejudiced: I'm keeping an open mind about my future. ∎  (open to) receptive to: the union was open to suggestions for improvements. ∎  (open to) admitting of; making possible: the message is open to different interpretations. ∎  freely available or accessible; offered without restriction: the service is open to all students at the university. ∎  with no restrictions on those allowed to attend or participate: an open audition was announced. ∎  (also Open) (of an award or the competition for it) unrestricted as to who may qualify to compete: each horse had won two open races. ∎  (of a ticket) not restricted as to day of travel.6. Mus. (of a string) allowed to vibrate along its whole length. ∎  (of a pipe) unstopped at each end. ∎  (of a note) sounded from an open string or pipe.7. (of an electrical circuit) having a break in the conducting path.8. Math. (of a set) not containing any of its limit points.• v. [tr.] 1. move or adjust (a door or window) so as to leave a space allowing access and view: she opened the door and went in | [intr.] “Open up!” he said. ∎  [intr.] (of a door or window) be moved or adjusted to leave a space allowing access and view: the door opened and a man came out. ∎  undo or remove the lid, cover, or fastener of (a container) to get access to the contents: he opened a bottle inexpertly, spilling some of the wine. ∎  remove the covers or wrapping from: can we open the presents now? ∎  part the lips or lids of (a mouth or eye): she opened her mouth to argue. ∎  [intr.] (of the mouth or eyes) have the lips or lids parted in this way: her eyes slowly opened. ∎  (of a wound) lose or lack its protective covering: old wounds opened and I bled a little bit. ∎  improve or make possible access to or passage through: the president announced that his government would open the border. ∎  cause evacuation of (the bowels). ∎  [intr.] (open onto/into) (of a room, door, or window) give access to: beautiful French doors that opened onto a balcony. ∎  [intr.] (of a panorama) come into view; spread out before someone: stop to marvel at the views that open out below. ∎  Naut. achieve a clear view of (a place) by sailing past a headland or other obstruction: we shall open Simon's Bay at any minute now.2. spread out; unfold: the eagle opened its wings and circled up into the air the tail looks like a fan when it is opened out fully. ∎  [intr.] be unfolded; spread out to the full extent: the flowers never opened beyond narrow points. ∎  increase the spaces or gaps between elements of (something): spacing the scaffolds opens up the tree so light can penetrate. ∎  part the covers or display the contents of (a book or file) to read it: she opened her book at the prologue. ∎  [intr.] (open out) become wider or more spacious: the path opened out into a glade.3. allow public access to: one woman raised $731 by opening her home and selling coffee and tea. ∎  make available: the new plan proposed to open up opportunities to immigrants. ∎  make more widely known; reveal: the move may force the company to open up its plans for the future. ∎  [intr.] (open up) become more communicative or confiding: neither one of them had opened up to me about their troubles. ∎  make (one's mind or heart) more receptive or sympathetic: open your mind to what is going on around you. ∎  (open someone (up) to) make someone vulnerable to: the process is going to open them to a legal threat.4. establish (a new business, movement, or enterprise): they have opened a new restaurant across the street. ∎  [intr.] (of an enterprise, esp. a commercial one) be established: two new restaurants open this week. ∎  [intr.] (of a store, place of entertainment, etc.) be officially ready to receive customers or visitors; become ready for business: the mall didn't open until 10. ∎  take the action required to make ready for use: they have the $10 necessary to open a savings account click twice to open a file. ∎  [intr.] (of a meeting or a sporting or artistic event) formally begin: the incident occurred just before the Olympic Games were due to open. ∎  [intr.] (of a piece of writing or music) begin: the chapter opens with a discussion of Anglo-American relations. ∎  (open up) [intr.] (of a process) start to develop: a new and dramatic phase was opening up. ∎  officially or ceremonially declare (a building, road, etc.) to be completed and ready for use: we will have to wait until a new bypass is opened before we can tackle the problem of congestion. ∎  (of a counsel in a court of law) make a preliminary statement in (a case) before calling witnesses. ∎  [tr.] Bridge make (the first bid) in the auction.5. break the conducting path of (an electrical circuit): the switch opens the motor circuit. ∎  [intr.] (of an electrical circuit or device) suffer a break in its conducting path.• n. 1. (Open) a championship or competition with no restrictions on who may qualify to compete: the venue for the British Open.2. an accidental break in the conducting path for an electrical current.PHRASES: be open with speak frankly to; conceal nothing from: I had always been completely open with my mother.in (or into) the open out of doors; not under cover. ∎  not subject to concealment or obfuscation; made public: we have never let our dislike for him come into the open.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.open the door to see door.open someone's eyes see eye.open fire begin to shoot a weapon.an open mind see mind.with one's eyes open (or with open eyes) fully aware of the risks and other implications of an action or situation: I went into the job with my eyes open.with open arms see arm¹ .PHRASAL VERBS: open up begin shooting: the enemy artillery had opened up.open something up1. accelerate a motor vehicle.2. (of an athlete or team) create an advantage for one's side: he opened up a lead of 14–8.DERIVATIVES: o·pen·a·ble adj.o·pen·ness n.