a witness whose testimony is both relevant to the matter at issue and required in order to resolve the matter
双语例句
1
The material would be checked against the depositions from other witnesses.
这份材料会与其他证人的证词对照加以核对。
《柯林斯英汉双解大词典》
2
The commission held 19 days of hearings and interviews with more than 700 witnesses; it has pledged to release a trove of transcripts and other raw material online.