こっそり (kossori) Japanese meaning: stealthily | KotomoraHe slipped out of the room stealthily.
Usage patterns
こっそり〈場所〉に入るto sneak into a place
He sneaked into the room in the middle of the night.
こっそり〈物〉を持ち出すto secretly take something out
My little sister secretly took out some snacks.
こっそり〈場所〉を抜け出すto slip out of a place unnoticed
The students slipped out of the classroom unnoticed during class.