Which term denotes something that is unchangeable?

The term "immutable" specifically denotes something that is unchangeable or cannot be altered. In various contexts, especially in programming and philosophy, "immutable" refers to objects or concepts that remain constant and are not subject to modifications. For instance, in computer science, immutable data structures are those that, once created, cannot be changed, making them essential for avoiding unintended side effects in programs.

While "immaterial" refers to something that lacks a physical presence or is not material in nature, "imperishable" describes something that cannot perish or is resistant to decay but does not imply that it cannot change. "Imminent," on the other hand, refers to something that is about to happen and does not relate to the concept of changeability. Therefore, "immutable" is the most precise term to indicate something that remains unchanged.