the word 'unalterable' is a modern english formation built from classical components. the core 'alter' derives from the latin verb 'alterāre', meaning 'to change', which itself comes from 'alter', meaning 'other'. the negative prefix 'un-', of old english and ultimately proto-germanic origin, was prefixed to the adjective 'alterable'. 'alterable' itself is formed by adding the suffix '-able', from latin '-ābilis' via old french, which denotes capability. thus, the literal construction "not capable of being changed" maps directly and logically to its modern abstract meaning of permanence or immutability.

Structure: un (not) + alter (change) + able (capable of) un: a prefix of germanic origin (old english) meaning "not". alter: a root of latin origin (alterāre) meaning "to change". able: a suffix of latin origin (via old french) meaning "capable of, fit for".