Definitions of replacement:

• noun:   the act of furnishing an equivalent person or thing in the place of another
• noun:   a person or thing that takes or can take the place of another
• noun:   a person who follows next in order
• noun:   someone who takes the place of another person
• noun:   filling again by supplying what has been used up
• noun:   an event in which one thing is substituted for another

  Example: "The replacement of lost blood by a transfusion of donor blood"