1. adjective /ɪmˈpɒsəbl,ɪmˈpɑsəbl/
a) Not possible, not able to be done.
Nothing is impossible, only impassible. , Alice in Wonderland
b) Of a person, very difficult to deal with.
It is difficult, if not impossible, to memorise 20,000 consecutive numbers.
2. noun /ɪmˈpɒsəbl,ɪmˈpɑsəbl/
a) An impossibility.
If we work together, we can achieve the impossible!
b) (with definite article) That which seems impossible.
Wikipedia foundation.