"Un trueness" is not a commonly used word, but it is spelled with the prefix "un-" which means "not", followed by the noun "trueness" which means the quality of being true or accurate. The correct pronunciation of this word is /ʌn ˈtruːnəs/, with the stress on the second syllable of "trueness". The "u" sound in the first syllable is a short u as in "umbrella", whereas the "oo" sound in the second syllable is a long u as in "truth".