Cruel, assiduous, cold-blooded, and cold-hearted are all synonyms for relentless. Short-lived, irresolute, and intermittent are these antonyms of relentless. And here are another 87 synonyms for relentless.
Relentless Synonyms
1. constant
- Assiduous
- Constant
- Continual
- Continuing
- Continuous
- Determined
- Diligent
- Dogged
- Endless
- Importunate
- Incessant
- Indefatigable
- Insistent
- Interminable
- Intransigent
- Lasting
- Never-ending
- Non-stop
- Obstinate
- Patient
- Perpetual
- Persevering
- Persistent
- Pertinacious
- Purposeful
- Resolute
- Sedulous
- Single-minded
- Steady
- Stubborn
- Sustained
- Tenacious
- Tireless
- Unabated
- Unabating
- Unbroken
- Unceasing
- Undeviating
- Unending
- Unfaltering
- Unflagging
- Uninterrupted
- Unrelenting
- Unrelieved
- Unremitting
- Unstoppable
- Unswerving
- Untiring
- Unwavering
- Obdurate
2. fierce
- Cold-blooded
- Cold-hearted
- Cruel
- Fierce
- Grim
- Hard-hearted
- Hard
- Harsh
- Heartless
- Inexorable
- Inflexible
- Lacking compassion
- Merciless
- Obdurate
- Pitiless
- Punishing
- Remorseless
- Ruthless
- Severe
- Stony-hearted
- Stony
- Strict
- Unbending
- Uncaring
- Uncharitable
- Uncompromising
- Unfeeling
- Unforgiving
- Unmerciful
- Unmoved
- Unpitying
- Unsparing
- Unsympathetic
- Unyielding
- With a heart of stone
- Implacable