Unsolved [adjective]
Definition of Unsolved:
mysterious, unable to be solved or answered
Sentence/Example of Unsolved:
Tea-time found him still wrestling with the unsolved problem.
To what extent this fish is amenable to the influences of temperature is an unsolved problem.
This question was yet unsolved in my mind as I drove into the court-yard of the palace.
To me, this has always been one of the unsolved mysteries of the book-mania.
There have been unsolved mysteries, but no man may say when a crime is unsolvable.
Chartreuse is the unsolved enigma of French compounders of liqueurs.
Further, there is also the important question yet unsolved, as to what Matter is.
And that is why the mystery of the Black Killer is yet unsolved in the Daleland.
There is an unsolved mystery about the tragedies and comedies that go on every spring.
It is at this point we reach the difficult and unsolved part of the problem.