Definition of relentful in US English:

relentful

adjective

rare
  • Sorrowful, softened, yielding, relenting. In later use humorous.

Origin

Late 16th century; earliest use found in George Chapman (?1560–1634), poet and playwright. Partly from relent + -ful, and partly from relent + -ful. In later use humorously after relentless.

Pronunciation

relentful

/rɪˈlɛntf(ʊ)l/