脑袋 (nǎo dai): đầu

He ran for too long; his head was covered in sweat, and his clothes were soaked through.

My younger brother accidentally bumped into the door frame and a big bump swelled up on his head.

Work has been so busy these days that my head is full of numbers and reports; even in my dreams I'm in meetings.

Grandpa is getting old, and sometimes his mind isn't very clear; he forgets where he put something right after setting it down.