From WordNet (r) 2.0 (August 2003) [wn]:
impossible
adj 1: not capable of occurring or being accomplished or dealt
with; "an impossible dream"; "an impossible situation"
[ant: possible]
2: totally unlikely [syn: inconceivable, {out of the
question}, unimaginable]
3: used of persons or their behavior; "impossible behavior";
"insufferable insolence" [syn: insufferable,
unacceptable, unsufferable]
n : something that cannot be done; "his assignment verged on the
impossible"
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Impossible \Im*pos"si*ble\, a. [F., fr. L. impossibilis; pref.
im- not + possibilis possible. See Possible.]
Not possible; incapable of being done, of existing, etc.;
unattainable in the nature of things, or by means at command;
insuperably difficult under the circumstances; absurd or
impracticable; not feasible.
[1913 Webster]
With men this is impossible; but with God all things
are possible. --Matt. xix.
26.
[1913 Webster]
Without faith it is impossible to please him. --Heb.
xi. 6.
[1913 Webster]
Impossible quantity (Math.), an imaginary quantity. See
Imaginary.
Syn: See Impracticable.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Impossible \Im*pos"si*ble\, n.
An impossibility; as, he tried to do the impossible. [Obs.]
[1913 Webster]
"Madam," quoth he, "this were an impossible!"
--Chaucer.
[1913 Webster]