Crack

1. To break without separating. The engine developed a crack from the freezing weather.
2. Highly trained and competent. It was a crack team of investigators.
3. Excellent, first-rate, superior. She's a crack shot with a rifle.
4. A narrow opening. He squeezed though the crack in the wall.
5. A humorous remark. She made a crack about my hair.
6. The sharp sound made when solid material breaks. I heard a crack just as the window shattered.
7. Any sharp sound. Crack! A sound that any soldier dreads.