Noun

1. An open or empty space in or between things
2. A ceremony accompanying the start of some enterprise
3. Becoming open or being made open
4. The first performance (as of a theatrical production)
5. The act of opening something
6. Opportunity especially for employment or promotion
7. The initial part of the introduction
8. A possible alternative
9. An aperture or hole that opens into a bodily cavity
10. A vacant or unobstructed space that is man-made
11. An entrance equipped with a hatch; especially a passageway between decks of a ship
12. A recognized sequence of moves at the beginning of a game of chess
13. The first of a series of actions

Adjective

1. First or beginning

Verb

1. Cause to open or to become open
2. Start to operate or function or cause to start operating or functioning
3. Become open
4. Begin or set in action, of meetings, speeches, recitals, etc.
5. Spread out or open from a closed or folded state
6. Make available
7. Become available
8. Have an opening or passage or outlet
9. Make the opening move
10. Afford access to
11. Display the contents of a file or start an application as on a computer