Definition of white elephant noun from the Oxford Advanced American Dictionary

 

white elephant

 noun
noun
 
[usually singular]
 
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a thing that is useless and no longer needed, although it may have cost a lot of money The new office building has become an expensive white elephant. From the story that in Siam (now Thailand) the king would give a white elephant as a present to someone that he did not like. That person would have to spend all their money on looking after the rare animal.
See the Oxford Advanced Learner's Dictionary entry: white elephant