Lexical Definition

‎ἀμετάθετος‎ ametáthetos (am-et-ath'-et-os) unchangeable ^G:A
from ‎Α‎ (as a negative particle) and a derivative of ‎μετατίθημι‎

immutable(-ility).

• unchangeable, or (neuter as abstract) unchangeability

Abbott-Smith

*† ἀ-μετάθετος, -ον (< μετατίθημι), [in LXX: III Mac 5:1,12*;]
immutable: He 6:18; as subst., τὸ ἀ., immutability, He 6:17 (v. MM, VGT, s.v.).†

Abbott-Smith References

Liddell-Scott-Jones

ἀμετάθετος-θετος, ον,

unalterable, immutable, κατάληψις, of knowledge, [Refs 4th c.BC+]; of fate, Chrysipp.[Refs 2nd c.BC+], etc. adverb -τως, διακεῖσθαι[Refs 1st c.BC+]

__2 Grammars, not inflected, [Refs 2nd c.AD+]