margin of safety, available amount of freedom or room to move or act
Weatherward or windward is the side of the ship toward the wind. The lee side is the side of the ship sheltered. Much like the leeward side of island is one that faces away from the wind and provides shelter. On the otherhand, a lee shore is downwind of the ship, i.e. facing the wind, and if there is not enough leeway then the ship can be driven onto shore.