Main entry: unalterable, changeless
Definition: remaining the same for indefinitely long times
Main entry: immutable, changeless
Definition: not subject or susceptible to change or variation in form or quality or nature
Usage: the view of that time was that all species were immutable, created by God
Main entry: invariant, unvarying, changeless, constant
Definition: unvarying in nature
Usage: maintained a constant temperature; principles of unvarying validity