definition of
substitution

[1] #1 substitution n. [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". wn

[2] #2 substitution n. [exchange, commutation] the act of putting one thing or person in the place of another: "he sent Smith in for Jones but the substitution came too late to help". wn