Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

testiere
     n : medieval plate armor to protect a horse's head [syn: {chanfron},
          {chamfron}, {frontstall}, {front-stall}]