Definitions of opening:

• noun:   the act of opening something

  Example: "The ray of light revealed his cautious opening of the door"

• noun:   becoming open or being made open

  Example: "The opening of his arms was the sign I was waiting for"

• noun:   a vacant or unobstructed space that is man-made

  Example: "They left a small opening for the cat at the bottom of the door"

• noun:   the initial part of the introduction

  Example: "The opening established the basic theme"

• noun:   the first performance (as of a theatrical production)

  Example: "The opening received good critical reviews"

• noun:   a ceremony accompanying the start of some enterprise
• noun:   an open or empty space in or between things

  Example: "There was a small opening between the trees"

• noun:   opportunity especially for employment or promotion

  Example: "There is an opening in the sales department"

• noun:   an entrance equipped with a hatch; especially a passageway between decks of a ship
• noun:   an aperture or hole opening into a bodily cavity
• noun:   a possible alternative
• noun:   the first of a series of actions

  Example: "He memorized all the important chess openings"

• adjective:   first or beginning

  Example: "The memorable opening bars of Beethoven's Fifth"