Etymology
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immutable (adj.)
early 15c., "unchanging, unalterable," from Old French immutable (Modern French immuable), and directly from Latin immutabilis "unchangeable, unalterable," from assimilated form of in- "not, opposite of" (see in- (1)) + mutabilis "changeable," from mutare "to change" (from PIE root *mei- (1) "to change, go, move"). Related: Immutably.
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immutability (n.)

1590s, from Latin immutabilitas "unchangeableness," from immutabilis "unchangeable" (see immutable).

Nought may endure but Mutability. [Shelley]
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*mei- (1)
Proto-Indo-European root meaning "to change, go, move," "with derivatives referring to the exchange of goods and services within a society as regulated by custom or law" [Watkins].

It forms all or part of: amiss; amoeba; azimuth; common; commune; communicate; communication; communism; commute; congee; demean; emigrate; emigration; excommunicate; excommunication; immune; immutable; incommunicado; mad; mean (adj.1) "low-quality;" mew (n.2) "cage;" mews; migrate; migration; mis- (1) "bad, wrong;" mistake; Mithras; molt; Mstislav; municipal; munificent; mutable; mutant; mutate; mutation; mutatis mutandis; mutual; permeable; permeate; permutation; permute; remunerate; remuneration; transmutation; transmute; zenith.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit methati "changes, alternates, joins, meets;" Avestan mitho "perverted, false;" Hittite mutai- "be changed into;" Latin mutare "to change," meare "to go, pass," migrare "to move from one place to another," mutuus "done in exchange;" Old Church Slavonic mite "alternately;" Czech mijim "to go by, pass by," Polish mijać "avoid;" Gothic maidjan "to change."
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sempiternal (adj.)

"eternal and unchanging, perpetual, everlasting," early 15c., from Old French sempiternel "eternal, everlasting" (13c.) or directly from Medieval Latin sempiternalis, from Latin sempiternus "everlasting, perpetual, continual," from semper "always, ever" (see semper-). Compare aeternus from aevum (for which see eternal). Related: Sempiternally.

Trawthe is immortalle, immutable, and sempiternalle.
[Higden's "Polychronicon," 15c. translation]
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