Related Clues:
- Enter, for one
- Crucially important, essential
- Coral reef off southern coast of Florida
- Absolutely necessary or life-giving
- Essential to life, indispensable
- Absolutely essential
- Essential to life or critically important
- Extremely important, essential to success
- Essential to life, most important
- Scale system for music
- It opens the door
- Urgently needed or absolutely necessary
- Essential to life, critically important
- Most important, like certain body organs
- Lock-opener