The word "utterness" is spelled with a double "t" and a single "n", even though it may feel more natural to spell it with two "n's". The reason for this is the pronunciation of the word. "Utterness" is pronounced /ˈʌtərnəs/ with a single "n" sound, not /ˈʌtnərnes/ with two "n" sounds. Therefore, the spelling reflects the pronunciation, as is the case with many words in the English language.