vain: implies either absolute or relative absence of value or worth: it's ~ to think we can alter destiny.


nugatory: suggests triviality or insignificance: a monarch with ~ powers.


otiose: suggests that something serves no purpose and is either an encumbrance or a superfluity: not a single scene in the film is ~.


idle: suggests a lack of capacity for worthwhile use or effect: it is ~ to speculate on what might have been.


empty, hollow: suggests a deceiving lack of substance, soundness, genuineness, or value: an ~ attempt at reconciliation (empty); a ~ victory that benefited no one (hollow).


vain: 泛指(either or)没有价值意义,较书面, nugatory: 琐屑、不重要, otiose:无用碍事或多余, idle: 泛指缺少效果作用,较口语, empty,hollow: 虚假的缺少实质价值的空洞


记忆方法：1）首字母VNOIEH重组为NO HIVE没有蜂箱<==空洞         hive蜂房蜂箱a structure made for bees to live in，还表示繁忙的地方
     
         2）空洞的意思是无价值或意义mean being without worth or significance.