发呆 (fā dāi)

to stare blankly; to be stunned; to be lost in thought

Character breakdown

发 (fā) · 5 strokes

Simplified form of both 發 (send out) and 髮 (hair). Visually similar to 犮, the bottom component of 髮.
呆 (dāi) · 7 strokes

Depicts the mouth (口) being stuck and not moving, like wood (木), representing someone stupid or expressionless.