elusive:difficult to find, define, or achieve 难找的;难以解释的;难以达到的
the elusive concept of 'literature' "文学"这一难以解释的概念 A solution to the problem of toxic waste is proving elusive in the extreme. 解决有毒废物的问题已证明极难实现. 来源:可可英语 //m.moreplr.com/kouyu/201001/94649.shtml