Unfeeling; pitiless; callous.
Inured; toughened.
Firmly established or unlikely to change; inveterate.
Having extra defences against attack; highly fortified.
Obstinately refusing to give up or let go.
Of data or a data structure: not transient or temporary, but remaining in existence after the termination of the program that creates it.
Describing a fractal process that has a positive Brown function
Lasting past maturity without falling off.
non-transient.
Insistently repetitive.
Indefinitely continuous.