Related Clues:
- The very beginning
- Maze entrance word
- "Boo!" reaction
- First square of some board games
- Sudden movement
- One maze terminal...
- Be part of the opening lineup
- Word next to an arrow, maybe
- Possible result of a gunshot
- Boot up
- With 21-Across, begin from scratch
- Outset
- Machine button
- Initial stage
- Turn a key, perhaps