History and sources

The forty-eighth entry is inverificável, the plainest word on the page in Portuguese and a small decision in English. Portuguese negates an adjective with one prefix and keeps using it: inverificável, incontestado, incompleto, inacabado, and a brand-new adjective can be given the same treatment tomorrow afternoon. English inherited that prefix as « in- », but it stopped growing centuries ago. It sits on words that arrived whole from Latin or French — « invisible », « incredible », « incontestable », « inaccessible » — and nothing new is ever added to it. The living prefix is the Germanic one, « un- », and it will take anything at all, including those same Latin stems: « unverifiable », « undocumented », « unattested », « undated », « unproven ». So the two adjectives that close this list, built identically in Portuguese, come out with different prefixes on the other side: inverificável is « unverifiable » and incontestado is « undisputed ». There is no rule to derive that from, and each word has to be learnt with its prefix attached. For anything modern or technical, « un- » is the safe guess.