say it: suhb-sti-TOO-shuhn
substitution is a noun meaning "an event in which one thing is substituted for another". It carries 2 recorded senses.
an event in which one thing is substituted for another
“the replacement of lost blood by a transfusion of donor blood”
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"
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for substitution come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.