An impossible task, an impossible request.
Walking to the moon is an example of something that would be described as impossible.
Someone who is really demanding, and who is never pleased no matter what, is an example of someone who would be described as impossible.
It is difficult, if not impossible, to memorize 20,000 consecutive numbers.
You never listen to a word I say – you're impossible!
If we work together, we can achieve the impossible!
An impossible goal.
An impossible child; an impossible situation.
Other Word Forms
Origin of impossible
From American Heritage Dictionary of the English Language, 5th Edition