Substitution

Noun

1. The act of substituting or the state of being substituted.

   "In this football tournament, three substitutions can be made during the match."

2. A substitute or replacement.

   "Gary is off this weekend, so Jeff will be his substitution."

3. The replacement of an atom, or group of atoms, in a compound, with another.
4. The expansion of the lexicon of a language by native means in correspondence to a foreign term.