Wiktionary
n. (context legal English) A statement that would normally be deemed inadmissible as evidence in a court of law as hearsay, but is deemed admissible because it was made by a person who believed himself to be dying, is about the circumstances of that person's death, and was followed by that person's actual death.
Wikipedia
In the law of evidence, the dying declaration is testimony that would normally be barred as hearsay but may in common law nonetheless be admitted as evidence in Criminal law trials because it constituted the last words of a dying person. The rationale, accurate or not, is that someone who is dying or believes death to be imminent would have less incentive to fabricate testimony, and as such, the hearsay statement carries with it some reliability.
Usage examples of "dying declaration".
The scientists foregathered there were left with his corpse (which was neatly taken care of by the CIA and the Effa Bee Eye) and that strange and awful dying declaration: It's eternity in there.
They had come upon Harold and his pitiful dying declaration the day after they had done the Eisenhower Tunnel.
Talia looked at William and her lips were motionless, but he could still hear her dying declaration in his mind.
Underwood's dying declaration: So you understand that when we increase the number of variables, the axioms themselves never change.
As the bus rolled past him at a steady fifteen miles an hour, Clay saw the man's face was drawn down in a grimace of fury and his mouth was working as he spewed out what was almost surely his dying declaration.
His dying declaration had suggested a rare modern case of lycanthropy, the knowledgeable agreed.
dying declarations are admissible when a person making them knows he is going to die, but this wasn't a dying declaration.
Sad as it was, it made this document something akin to a dying declaration, therefore, arguably, admissible in federal district court as evidentiary material in a criminal case.