relentless

形容词 relentless:

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

1. He was relentless in demanding repayment of the debt.
   他冷酷无情地要求偿还那笔债。

re.lent.less

adj.（形容词）
Unyielding in severity or strictness; unrelenting:
无情的：在严酷或严格方面不屈从的，不宽容的：
例句：
relentless persecution.
无情的迫害

Steady and persistent; unremitting:
持续不断的：稳定的和持续的；不松懈的：
例句：
the relentless beat of the drums.
持续不断的击鼓声

【引伸】
relent.lessly
adv.（副词）
relent.lessness
n.（名词）