Seshachalmak,
I'm not using the PMBOK 7th as a guide, but here are what I consider to be the main differences:
Stewardship is taking care of something, usually property. It is taking care of that "something" in the place of the owner - i.e. the owner's personal representative in matters pertaining to that property. The focus of the steward is to maximize the utilization of that "something" for the benefit of the owner. A more solid example may be a project budget: It's not YOUR money, but you've been entrusted with that money to maximize its use for the company.
Leadership is an act of getting a group of people to move cohesively as a unit to accomplish a goal.
Hope that helps,
Harry
