A witness whose testimony is both relevant to the matter at issue and required in order to resolve the matter.

Roget 467: evidence; facts, premises, data, praecognita [Lat.], grounds.    indication etc. 550; criterion etc. (test) 463.    testimony, testification^†, expert testimony; attestation; deposition etc. (affirmation) 535; examination.    admission etc. (assent) 488; authority, warrant, credential, diploma, voucher, certificate, doquet^†, docket; testamur^†; record etc. 551; document; pi ce justificative^†; deed, warranty etc. (security) 771; signature, seal etc. (identification) 550; exhibit, material evidence, objective evidence.    witness, indicator, hostile witness; eyewitness, earwitness, material witness, state's evidence; deponent; sponsor; cojuror^†.    oral evidence, documentary evidence, hearsay evidence, external evidence, extrinsic evidence, internal evidence, intrinsic evidence, circumstantial evidence, cumulative evidence, ex parte evidence [Lat.], presumptive evidence, collateral evidence, constructive evidence; proof etc. (demonstration) 478; evidence in chief.    secondary evidence; confirmation, corroboration, support; ratification etc. (assent) 488; authentication; compurgation^†, wager of law, comprobation^†.    citation, reference; legal research, literature search (experiment) 463.    ... show more