
n. a person who apparently has information about the subject matter of a lawsuit or criminal prosecution which is significant enough to affect the outcome of the case or trial. Thus, the court must make every reasonable effort to allow such a witness to testify, including a continuance (delay in a trial) to accommodate him/her if late or temporaril...
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http://dictionary.law.com/Default.xhtml?selected=1225

(n) Material witness is the person who can give worthy information or significant evidence about the subject matter of the law suit, which have important bearing on the outcome of the trial. Eg. Eye witness of the incident.
Found on
http://www.encyclo.co.uk/local/21213

A witness who has significant information about the subject matter of a lawsuit or criminal prosecution, particularly when few, if any other witnesses have the same knowledge. Judges usually make every reasonable effort to allow such a witness to testify, including granting a continuance (delaying a trial) to accommodate the witness.
Found on
http://www.nolo.com/dictionary/material-witness-term.html

[
n] - a witness whose testimony is both relevant to the matter at issue and required in order to resolve the matter
Found on
http://www.webdictionary.co.uk/definition.php?query=material%20witness
noun a witness whose testimony is both relevant to the matter at issue and required in order to resolve the matter
Found on
https://www.encyclo.co.uk/local/20974

person whose testimony on some issue has been judicially determined as relevant and substantial
Found on
https://www.encyclo.co.uk/local/22316
No exact match found.