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, James Ryder Randall, “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
   • 1906, Lord Dunsany [i.e., Edward Plunkett, 18th Baron of Dunsany], Time and the Gods‎, London: William Heineman, →OCLC, page 5:

     Tears may not bring again Sardathrion. But this the gods may do who have seen, and seen with unrelenting eyes, the sorrows of ten thousand worlds—thy gods may weep for thee.

• 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, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.