形容詞 relentless:

1. not to be placated or appeased or moved by entreaty
   同義詞：grim, inexorable, stern, unappeasable, unforgiving, unrelenting
2. never-ceasing
   同義詞：persistent, unrelenting

1. He was relentless in demanding repayment of the debt.
   他冷酷無情地要求償還那筆債。

re.lent.less

adj.（形容詞）
Unyielding in severity or strictness; unrelenting:
無情的：在嚴酷或嚴格方面不屈從的，不寬容的：
例句：
relentless persecution.
無情的迫害

Steady and persistent; unremitting:
持續(xù)不斷的：穩(wěn)定的和持續(xù)的；不松懈的：
例句：
the relentless beat of the drums.
持續(xù)不斷的擊鼓聲

【引伸】
relent.lessly
adv.（副詞）
relent.lessness
n.（名詞）