What does "deponent" mean?

Deponent: (Gr. & Lat. Gram.) A deponent verb. These are legal terms describing a person who makes a written declaration under oath, with a view to establish certain facts. An affiant is one who makes an affidavit, or declaration under oath, in order to establish the truth of what he says. A deponenet is one who makes a deposition, or gives written testimony under oath, to be used in the trial of some case before a court of justice. See under Deposition.