the.com/mercilessness

means The quality of showing no pity or compassion when inflicting punishment, harm, or judgment on someone.

from Built from 'merci' (mercy), which English borrowed from Old French 'merci' meaning pity or thanks, tracing back to Latin 'merces' meaning wages or reward — the word drifted from 'payment due' to 'a favor not strictly owed,' and finally to 'compassion shown where it needn't be.' Slap on the negating 'less' and the abstract-noun suffix '-ness,' and you get the state of being entirely without that unearned kindness — mercy's absence turned into its own cold, standalone condition.