SUBSTITUTE

Substitute refers to something that takes the place of something else. It can denote a person or thing that acts in place of another, on a temporary or provisional basis. Examples include substitute teachers who stand in for regular instructors, and substitute players who enter games when others are unavailable or fatigued.

In mathematics and logic, substitution is the operation of replacing a variable or symbol with a value or expression. In solving equations, substitution can be used to replace one variable with an expression in terms of another. In logic, the substitution principle allows the replacement of equivalent expressions within a statement.

In chemistry, a substitution reaction is a chemical process in which one atom or group is replaced by another in a molecule, common in organic synthesis.

In economics and everyday usage, substitute goods are pairs of products that can satisfy the same need, so a rise in the price of one may increase demand for the other. Substitution also occurs in linguistics and semantics, where items may replace others in usage or form, such as morphological or lexical substitution for stylistic or efficiency reasons.

In sports, a substitute is a player who is not in the starting lineup but can enter the game. In medicine, substitution can refer to substituting one medication for another, under professional guidance.

Etymology: substitute derives from Latin substitutus, from sub- “under” and statuere “to set,” meaning placed in place of.