This word is acceptable for play in the UK dictionary that is being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. The state or condition of being unmerciful.

n. The character of being unmerciful; cruelty; inhumanity.

n. inhumaneness evidenced by an unwillingness to be kind or forgiving

"For the first time he felt, rid of all disguise, the unmercifulness which was imminent in this or that transgression of his."

inhumanity    inhumaneness   

pitilessness    inexorability    inexorableness    ruthlessness    relentlessness