ichidan verb, intransitive verb
sneak out; slip out; leave secretly
Describes leaving a place quietly and stealthily, often to avoid being noticed. Intransitive; the subject is the person who sneaks out.
会議中に彼はこっそり忍び出た。
He quietly slipped out during the meeting.
夜中に家を忍び出る
It's dangerous to sneak out of the house in the middle of the night.