double-lock

The buccaneer went out, shutting Croustillac in by means of a double lock.

They shut up and double lock the doors and windows of their cabins at night to keep out evil spirits.

He had written much poetry about Lily, but he kept his lines safe under double lock and key.

Finally the double lock gave way and Tommy and Frank were precipitated headlong into the brightly lighted room beyond.

I shall double-lock myself in with him and have it out before I die, I'm quite certain of it.'