How to say "relentless" in Japanese

Choosing the right word

冷酷れいこくJLPT N1approx.Common
na-adjective, nounCovers 'relentless' in the sense of merciless and coldhearted, describing a person or behavior that shows no pity. A typical context is a ruthless ruler or the cruel treatment of others.
犬いぬを叩たたくなんて彼かれは冷酷れいこくだ。↗
It was cruel of him to beat his dog.
厳しいきびしいJLPT N4approx.Common
i-adjectiveCovers 'relentless' as severe and unsparing: relentless demands or criticism that allow no letup. The emphasis falls on strictness and harshness rather than on cruelty or persistence.
彼かれは厳きびしい批判ひはんにさらされた。↗
He was subjected to severe criticism.
執拗しつようCommon
na-adjectiveThe closest match for 'relentless' as unceasing persistence: pursuit, questioning, or effort that never lets up. It highlights tenacity, sometimes with a shade of obstinacy.
彼女かのじょは彼かれの執拗しつようさにうんざりしていた。↗
She was disgusted at his persistence.

For 'relentless' as merciless cruelty use 冷酷; for relentless severity, as in unsparing demands or criticism, use 「厳しい」; for relentless persistence that never gives up, use 執拗.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

Japanese equivalents

冷酷れいこくcruelty
厳しいきびしいsevere
執拗しつようpersistent
絶えることなくたえることなくunceasing
激しいはげしいincessant

JLPT vocabulary levels are community estimates, not official (no official lists have been published since the 2010 revision).

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