Synonyms for Opening:

adj.

beginning (adjective)
initial, initiatory.
earliest (adjective)
original.

n.

abyss, blowhole, cavity, channel, chink, cleft, cranny, crater, primary. all along, at first, early, front end, initial, new, open, original, outlet, vent, from the get-go. appearance, arrival, birth, conception, dawn, genesis, nascence, nascency, onset, starting point. appointment, background, business, call, calling, career, collaboration, delegation, incipience, incipiency, kickoff, launch, origination, leadoff, division of labor. chance, choice, luck, occasion, opportunity, scope, shot, Possibilities, window of opportunity, the initiative. force, open up, pry, try, undo, unfold, unlock, unscrew, burst open, crack something open. beginning (noun)
birth, dawn, incipience, incipiency, kickoff, launch, onset, starting point, leadoff.
chance (noun)
occasion, opportunity, possibility, scope, shot.
entrance (noun)
access, aperture, door, entrance, entryway, ingress, input, intake.
gap, hole (noun)
aperture, cavity, chink, cleft, cranny, door, hatch, mouth, orifice, outlet, scuttle, vent.
introduction (noun)
forward, introduction, overture, preamble, preface, prelude, prologue.
object (noun)
gap.
opening (noun)
beginning, chasm, curtain raising, embouchure, first, first step, gap, gate, hatch, hatchway, inaugural, initiative, initiatory, inlet, introductory, maiden, mouth, opening move, opening night, orifice, pore, porta, portal, possibility, possible action, scuttle, starting, yawning.
premiere (noun)
opening night.

v.

opening (verb)
baring, disclosing, releasing, revealing, undoing, Exposing, uncorking, unlocking, unplugging, unsealing.

Other synonyms:

all along, front end, genesis, incipience, incipiency, nascence, nascency, opportunity, origination, leadoff, window of opportunity. kickoff, new, occasion, onset. dawn, original, outlet, scope. choice, shot. early, vent. birth, chance. Other relevant words:
abyss, access, appearance, appointment, arrival, background, beginning, birth, blowhole, business, call, calling, career, cavity, chance, channel, chink, choice, cleft, collaboration, conception, cranny, crater, curtain raising, dawn, delegation, early, first, first step, force, front end, genesis, hatchway, inaugural, incipience, incipiency, initial, initiative, initiatory, introductory, kickoff, launch, luck, maiden, nascence, nascency, new, occasion, onset, open, open up, opening move, opening night, opportunity, original, origination, outlet, porta, possibility, possible action, primary, pry, scope, scuttle, shot, starting, starting point, try, undo, unfold, unlock, unscrew, vent, Possibilities, leadoff, window of opportunity.

Usage examples for opening

  1. " It is one o'clock," he said, opening the door. – The Crooked House by Brandon Fleming
  2. John Sammons asked, his eyes opening wide in surprise. – The Minute Boys of the Mohawk Valley by James Otis
  3. Off with you through that opening – A Dash from Diamond City by George Manville Fenn