opening (n.)

Old English openung "act of making open" (a door, mouth, etc.), "disclosure, manifestation," verbal noun from present participle of open (v.). Meaning "vacant space, hole, aperture, doorway" is attested from c. 1200. Meaning "act of opening (a place, to the public)" is from late 14c.  Sense of "opportunity, chance" is from 1793. Sense of "action of beginning (something)" is from 1712; meaning "first performance of a play" is 1855; that of "start of an art exhibit" is from 1905. Opening night is attested from 1814.

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Definitions of opening from WordNet
opening (n.)
an open or empty space in or between things;
there was a small opening between the trees
Synonyms: gap
opening (n.)
a ceremony accompanying the start of some enterprise;
opening (n.)
becoming open or being made open;
the opening of his arms was the sign I was waiting for
opening (n.)
the first performance (as of a theatrical production);
the opening received good critical reviews
Synonyms: opening night / curtain raising
opening (n.)
the act of opening something;
the ray of light revealed his cautious opening of the door
opening (n.)
opportunity especially for employment or promotion;
there is an opening in the sales department
opening (n.)
the initial part of the introduction;
the opening established the basic theme
opening (n.)
a possible alternative;
Synonyms: possibility / possible action
opening (n.)
an aperture or hole that opens into a bodily cavity;
Synonyms: orifice / porta
opening (n.)
a vacant or unobstructed space that is man-made;
they left a small opening for the cat at the bottom of the door
opening (n.)
an entrance equipped with a hatch; especially a passageway between decks of a ship;
Synonyms: hatchway / scuttle
opening (n.)
a recognized sequence of moves at the beginning of a game of chess;
he memorized all the important chess openings
Synonyms: chess opening
opening (n.)
the first of a series of actions;
Synonyms: first step / initiative / opening move
opening (adj.)
first or beginning;
the play's opening scene
the memorable opening bars of Beethoven's Fifth