pitilessly vs unmercifully

pitilessly and unmercifully both are adverbs.

Word	Noun	Adjective	Verb	Adverb
pitilessly	No	No	No	Yes
unmercifully	No	No	No	Yes

As adverbs, pitilessly and unmercifully are synonyms defined as:

Other synonyms of pitilessly include mercilessly, remorselessly.

pitilessly (adverb)	unmercifully (adverb)
without pity; in a merciless manner	without pity; in a merciless manner