adjective
(usually not comparable) Physically unobstructed, uncovered, etc.
Able to be used or interacted with in some way.
Not hidden or restricted.
Not completed or finalised.
(mathematics, logic, of a formula) Having a free variable.
(mathematics, topology, of a set) Which is part of a predefined collection of subsets of X, that defines a topological space on X.
(music, stringed instruments) Of a note, played without pressing the string against the fingerboard.
(music) Of a note, played without closing any finger-hole, key or valve.
(phonetics, sometimes with comparative opener) Uttered with a relatively wide opening of the articulating organs; said of vowels.
(phonetics) Uttered, as a consonant, with the oral passage simply narrowed without closure.
(computing, used before "code") Source code of a computer program that is not within the text of a macro being generated.
(of a multi-word compound) Having component words separated by spaces, as opposed to being joined together or hyphenated; for example, time slot as opposed to timeslot or time-slot.
(especially sports) Of a club, bat or other hitting implement, angled upwards and/or (for a right-hander) clockwise of straight.
verb
To make or become physically unobstructed, uncovered, etc.
(transitive, intransitive) To cause or allow a gap to form or widen.
To make or become available for use or interaction.
To start or begin.
(transitive) To make an open relationship or marriage, i.e., with possible additional relationships.
(obsolete) To disclose; to reveal; to interpret; to explain.
noun
(in the definite) Open or unobstructed space; an exposed location.
(in the definite) Public knowledge or scrutiny; full view.
(electronics) A defect in an electrical circuit preventing current from flowing.
A sports event in which anybody can compete, especially or originally irrespective of amateur or professional status.
The act of something being opened, such as an e-mail message.