寝顔

1. Origins, structure, and basic meaning

• Structure: 寝顔(ねがお) is a noun for a person's face or expression while asleep.
• Basic usage: Connect the sleeper with の, as in 赤ん坊の寝顔 and 弟の寝顔.

2. Common pitfalls and similar expressions

• The sleeping state
  • It focuses on the face as it appears during sleep rather than on a person's face in general.
• Action and appearance
  • 眠る describes sleeping, while 寝顔 names the face visible in that state.