pie in the sky
空中楼阁，不大可能实现的允诺
释义：
something that you hope will happen but is very unlikely to happen 渺茫的希望;不大可能实现的计划/允诺
例句：
Their plans to set up their own business are just pie in the sky.
The true regeneration of devastated Docklands seemed like pie in the sky.
