unrelenting

un- +‎ relenting

unrelenting (comparative more unrelenting, superlative most unrelenting)

1. Not relenting; not yielding in strength, severity, or determination.

   Synonyms: unyielding, brutal, hard, harsh, stern, cruel

   • 1908, Randall, James Ryder, “There’s Life in the Old Land Yet”, in Maryland, my Maryland, and other poems, Baltimore, Md.; New York: John Murphy Company, page 23:

     There’s faith in their unrelenting woes, / There’s Life in the Old Land yet!

2. Having no pity; not being or becoming lenient, mild, gentle, or merciful

• relentless

• relent
• unrelentingly
• unrelentingness

• “unrelenting”, in The Century Dictionary […], New York, N.Y.: The Century Co., 1911, →OCLC.
• unrelenting in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913