ADJ （支持、努力、热情等）不懈的，持续的 If you describe something such as support, effort, or enthusiasm as unflagging, you mean that it does not stop or get less as time passes. （支持、努力、热情等）不懈的，持续的 [approval]
He was sustained by the unflagging support of his family.
他得到了家人不断的支持。
...unflagging optimism.
不变的乐观
The book is not one word too long and its narrative pace is unflagging.