late 14c., "unfeeling, pitiless, cruel," from mercy + -less. Sense of "relentless" is from early 15c.; of inanimate things, from 1580s. Related: Mercilessly; mercilessness.
gave him a merciless beating
the merciless enemy
a merciless critic
merchandizing
merchant
merchantman
Mercia
merciful
merciless
mercurial
mercuric
Mercury
mercury
mercy
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