noun.
A trial that is rendered void and of no legal effect because of some serious procedural error or irregularity or because of the inability of the jury to reach a verdict.
The Century Dictionary and Cyclopedia
noun.
In law: A trial the result of which is vitiated by errors, as by disqualification in a juror or in the judge.
noun.
More loosely, an inconclusive trial; a trial that fails to issue in a decision, as where the jury cannot agree.
the GNU version of the Collaborative International Dictionary of English
noun.
A false or erroneous trial; a trial which has no result; a trial which comes to no conclusion, such as a criminal trial which does not produce a unanimous verdict of the jurors.