隙

1. Origins, structure, and basic meaning

• Structure: 隙(すき) is a noun for a physical gap or an opening caused by weakened defense or attention.
• Basic usage: A physical gap appears in 扉の隙, while a defensive opening appears in 守りに隙ができる.

2. Common pitfalls and similar expressions

• Space and vulnerability
  • Context distinguishes an actual opening that lets light through from a weakness that an opponent can exploit.
• Particle choice
  • Use 扉の隙 for a gap in a door and 守りに隙ができる for an opening developing in a defense.