immūtābĭlĭtas (inm-), ātis, f. [1. immutabilis],
unchangeableness , immutability : in factis immutabilitatem apparere, in futuris non item, Cic. Fat. 9, 17.
immūtābilitās (inm-) ātis, f immutabilis, unchangeableness, immutability . ...
An Elementary Latin Dictionary