promise the moon/earth/world

promise the moon (to someone)

 and promise someone the moon
to make extravagant promises to someone. Bill will promise you the moon, but he won't live up to his promises. My boss promised the moon, but never gave me a raise.
See also: moon, promise

promise the earth

If someone promises the earth, they promise to give people things that they cannot in fact possibly give them. `Politicians have lost credibility,' he complained, `they promise the earth and don't deliver.'
See also: earth, promise

promise the moon

If someone promises the moon, they promise to do or give things that they cannot in fact give. Politicians promise the moon at election time, but do they deliver once they're elected?
See also: moon, promise

promise (somebody) the ˈmoon/ˈearth/ˈworld

(informal) make very big or impossible promises that you are unlikely to keep: He promised her the moon, but after ten years of marriage they hardly had enough to live on.
See also: earth, moon, promise, world