1590s, from Latin immutabilitas, from immutabilis (see immutable).
Nought may endure but Mutability. [Shelley]
early 15c., from Old French immutable and directly from Latin immutabilis "unchangeable," from assimilated form of in- "not, opposite of" (see in- (1)) + mutabilis "changeable," from mutare "to change" (see mutable). Related: Immutably.