Synonyms for Impossible:
foolish, invalid, preposterous, irrational, nonsensical, implausible, contradictory, incongruous, ludicrous, eccentric, senseless, farcical, silly, meaningless, illogical, inconsistent, anachronistic, fallacious, inane, bizarre, ridiculous, idiotic, paradoxical, crazy, outlandish, absurd, self-contradictory.
•beyond the bounds of possibility (adjective)
impracticable, unobtainable, inaccessible, hopeless, unworkable, insurmountable, futile, preposterous, unfeasible, unattainable, impractical, infeasible, unthinkable, unimaginable, useless, unachievable, no-go, absurd, out of the question, inconceivable, impassable.
unattainable, absurd, impracticable, implausible, unfeasible, unobtainable, inconceivable, unworkable.
•intolerable, ungovernable (adjective)
ludicrous, undesirable, improper, unsuitable, objectionable, offensive, incongruous, unacceptable.
n.difficult, delicate, critical, thorny, intractable, awkward, trying, improbable, unlikely, testing. hardly, unbelievable, no-go, something will not work/start/open etc., offensive, unsuitable, possibly, objectionable, with the best will in the world, be out of the question, undesirable, impossibility, improper. irritable, unmanageable, obstinate. impractical. insupportable, unbearable, unendurable, unsupportable, pain. balky, wayward, contrary, attitude, perverse, froward, support, contrarious, ornery. •impossible (noun)
intolerable, unattainable, hopeless, unacceptable, unachievable, unworkable, out of the question, undoable, unfeasible, impracticable, out, unimaginable, infeasible, inconceivable, unrealizable, insufferable, unsufferable.
impossibility, unsupportable, ornery, contrarious. intractable, insupportable, froward, unbelievable, thorny, balky, unendurable, testing, wayward, unbearable. contrary, inaccessible. critical, possibly, perverse. delicate, difficult. •discouraging
•Other relevant words:
delicate, unacceptable, critical, futile, insupportable, impossibility, unmanageable, unrealizable, hopeless, out of the question, likely, ornery, insufferable, untenable, undesirable, unbelievable, perverse, unlikely, unbearable, awkward, insurmountable, thorny, out, wayward, obstinate, offensive, unsupportable, unachievable, vain, undoable, impractical, froward, difficult, trying, unendurable, balky, unimaginable, possibly, unsuitable, objectionable, no-go, incredible, intolerable, improbable, infeasible, inaccessible, impassable, unsufferable, contrary, useless, improper, unthinkable, intractable, contrarious.