What does immutable mean?
Immutable means unable to be changed, altered, or modified. The word is used for things whose nature or condition is regarded as fixed, whether by principle, law, design, or physical reality. In philosophy and law, describing something as immutable can imply that admitting change would undermine a fundamental rule or certainty. In computing, immutable data or objects are designed so that their contents cannot be modified after creation, which can make programs easier to reason about and safer to share. Unlike a word such as difficult, immutable does not suggest that change is merely hard; it indicates that change is not possible or not permitted. The adjective has a formal, authoritative tone and is especially useful when discussing permanence, integrity, and the preservation of original information.
adjectiveUnable to be changed, altered, or modified; unchanging or fixed.
- Unchanging over time or impossible to alter.
- Fixed by nature, principle, or design, so that modification is not permitted.
"In a well-designed system, immutable records preserve the original event exactly as it occurred."
"The court's decision is not immutable; new evidence can reopen the question."
"Immutable data structures help programmers reason about values without accidentally changing them."
The word is a linguistic lock: it combines a negative prefix with the same Latin root found in mutate and mutation, literally meaning “not changeable.”
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does immutable come from?
The English adjective comes from Latin immutabilis, a form meaning “not changeable,” built from the negative prefix in- and mutabilis, “changeable.” The root ultimately comes from Latin mutare, “to change,” which also underlies English words such as mutate and mutation. Its Latin formation became English immut-, while the ending -able preserves the adjective-forming sense of “capable of being” or “liable to be.”
Related word forms
How immutable is actually used
The word is formal and common in legal, philosophical, scientific, and computing contexts. It is stronger than merely saying that something is difficult to change: it asserts that change is impossible or prohibited.
Easily confused with immutable
Mutable means capable of being changed, whereas immutable means incapable of change.