replacement, replacing -- (the act of furnishing an equivalent person or thing in the place of another; "replacing the star will not be easy")
surrogate, alternate, replacement -- (someone who takes the place of another person)
substitution, permutation, transposition, replacement, switch -- (an event in which one thing is substituted for another; "the replacement of lost blood by a transfusion of donor blood")
substitute, replacement -- (a person or thing that takes or can take the place of another)