The spelling of the word "fellest" is derived from the root word "fell", meaning cruel or fierce. The -est suffix is added to indicate the superlative form, making "fellest" mean the most cruel or fierce. The pronunciation of "fellest" is /ˈfel.ɪst/, with the stress on the first syllable. The "f" sound is represented by the letter "f", the "e" sound is represented by the letter "e", the "l" sound is represented by the letter "l", and the "st" sound is represented by the letters "st".