barmecide

n.

[A prince of the Barmecide family, who, as related in the «Arabian Nights' Tales», pretended to set before the hungry Shacabac food, on which the latter pretended to feast.]
One who proffers some illusory advantage or benefit. Also used as an adj.: Barmecidal. «A Barmecide feast.» Dickens.

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[adj] illusory, imaginary; such as to disappoint
[n] a giver of benefits that are illusory or disappointing