'untestability' originates from English, formed by the prefix 'un-' (meaning 'not') attached to 'testability', where 'testability' itself is derived from 'test' + the suffix '-ability'.

'test' ultimately comes from Latin 'testari' (to bear witness) via Old French and Middle English; the adjective 'testable' and noun 'testability' developed with the suffix '-able'/'-ability', and modern English formed 'untestability' by adding the privative prefix 'un-'.

The element 'testability' originally meant 'the quality of being able to be tested'; adding 'un-' reversed this to mean 'the quality or state of not being able to be tested', which is the current meaning of 'untestability'.