The spelling of the word "Fellness" is unique and not commonly used in the English language. It is pronounced as /ˈfɛlnəs/ which means that the first syllable "fell" is pronounced as "fɛl" and the second syllable "ness" is pronounced as "nəs". The IPA phonetic transcription helps to break down the pronunciation of the word into individual sounds. While the spelling of "Fellness" may be unusual, it can still be understood through its phonetic transcription.
Cruelty.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.