The Collaborative International Dictionary of English v.0.48:
Testiere \Tes`ti*[`e]re"\, n. [OF. testiere. See Tester a headpiece.] A piece of plate armor for the head of a war horse; a tester. [1913 Webster]WordNet (r) 3.0 (2006):
testiere n 1: medieval plate armor to protect a horse's head [syn: chanfron, chamfron, testiere, frontstall, front- stall]