Nautiterm: (Nautical Terms Explained) “Give me some slack”

Make allowances for the completion of an act
It took teams of men to haul in and tie a ship to a pier. As one team hauled on their line, tension on the other line was released (the second team were therefore 'given slack'), and so on until the ship was properly aligned. A variation of this expression in modern use is 'cut me some slack'.