Adjective

(en adjective)

Not certain; unsure.

*(John Tillotson) (1630-1694)

*:Man, without the protection of a superior Being,is uncertain of everything that he hopes for.

Not known for certain; questionable.

:

Not yet determined; undecided.

Variable and subject to change.

Fitful or unsteady.

*

*:Turning back, then, toward the basement staircase, she began to grope her way through blinding darkness, but had taken only a few uncertain steps when, of a sudden, she stopped short and for a little stood like a stricken thing, quite motionless save that she quaked to her very marrow in the grasp of a great and enervating fear.

Unpredictable or capricious.

*Sir (Walter Scott) (1771-1832)

*:O woman! in our hours of ease, / Uncertain , coy, and hard to please!

Adjective

(en adjective)

Not possible; not able to be done or happen.

* 1865 , (Lewis Carroll), (w, Alice's Adventures in Wonderland)

Nothing is impossible , only impassible.

* 13 March 1962 ,

Those who make peaceful revolution impossible will make violent revolution inevitable.

* {{quote-magazine, date=2013-06-28, author=(Joris Luyendijk)

, volume=189, issue=3, page=21, magazine=(The Guardian Weekly) , title= Our banks are out of control , passage=Seeing the British establishment struggle with the financial sector is like watching an alcoholic […].  Until 2008 there was denial over what finance had become. When a series of bank failures made this impossible , there was widespread anger, leading to the public humiliation of symbolic figures.}}

(colloquial, of a person) Very difficult to deal with.

(math, dated) imaginary

impossible quantities, or imaginary numbers