INCOMMUTABLE
incommutable
(adjective) not subject to alteration or change
incommutable
(adjective) not interchangeable or able to substitute one for another; “a rare incommutable skill”
Source: WordNet® 3.1
Etymology
Adjective
incommutable (not comparable)
Not commutable
Source: Wiktionary
In`com*mut"a*ble, a. Etym: [L. incommutabilis: cf. F. incommutable.
See In- not, and Commutable.]
Definition: Not commutable; not capable of being exchanged with, or
substituted for, another. Cudworth.
– In`com*mut"a*ble*ness, n.
– In`com*mut"a*bly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition