IPA: //səbˈstɪtʃʊtɪv//
KK: /sʌbˈstɪtʃʊtɪv/
This word describes something that can be used in place of another thing.
In cooking, a substitutive ingredient can replace the original one if it's not available.
Substitutive → It is formed from "sub-" (meaning under or in place of) and "stituere" (meaning to place or set). The word "substitutive" refers to something that is placed in the place of another.
Think of something being placed 'in place of' ('sub-') another thing — that's why 'substitutive' means serving as a replacement.