You describe something as regrettable when you think that it is bad and that it should not happen or have happened.
例句
...an investigation into what the army described as a regrettable incident...对军方称之为令人遗憾的事件的调查It is regrettable that strike leaders seem intent on spoiling holidays.遗憾的是罢工领导人似乎决意要破坏节日的气氛。
英汉词典释义
adv.
抱歉地,遗憾地,可悲地
He said that they had regrettably been obliged to give up the scheme for lack of support.他说因为缺乏支持,他们遗憾地被迫放弃了这项计划。
英英词典释义
Adverb
1. by bad luck;
"unfortunately it rained all day""alas, I cannot stay"