unmercifully vs pitilessly

unmercifully and pitilessly both are adverbs.

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

As adverbs, unmercifully and pitilessly are synonyms defined as:

Other synonyms of unmercifully include mercilessly, remorselessly.

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