The Collaborative International Dictionary of English v.0.48:
Unmerciful \Un*mer"ci*ful\, a. Not merciful; indisposed to mercy or grace; cruel; inhuman; merciless; unkind. -- Un*mer"ci*ful*ly, adv. -- Un*mer"ci*ful*ness, n. [1913 Webster]WordNet (r) 3.0 (2006):
unmercifully adv 1: without pity; in a merciless manner; "he was mercilessly trounced by his opponent in the House" [syn: mercilessly, pitilessly, unmercifully, remorselessly]