The Collaborative International Dictionary of English v.0.48:
Testifier \Tes"ti*fi`er\, n. One who testifies; one who gives testimony, or bears witness to prove anything; a witness. [1913 Webster]WordNet (r) 3.0 (2006):
testifier n 1: a person who testifies or gives a deposition [syn: testifier, deponent, deposer]