- Spread out. 2. Begin operation. 3. Begin attacking. 4. Speak freely and candidly. 5. Open a door when asked. 6. Become available or accessible. 7. Increase a vehicle's speed.
Examples:
- A green valley opened up before us.
- At last the witness opened up and told what happened.
- Open up! This is the police.
Origin: Early 1800s (sense 1); Late 1700s (sense 2); 1930s (sense 3); c. 1920 (sense 4)