The Collaborative International Dictionary of English v.0.48:

Trier \Tri"er\, n. [From Try.]
   1. One who tries; one who makes experiments; one who examines
      anything by a test or standard. --Boyle.
      [1913 Webster]

   2. One who tries judicially.
      [1913 Webster]

   3. (Law) A person appointed according to law to try
      challenges of jurors; a trior. --Burrill.
      [1913 Webster]

   4. That which tries or approves; a test. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

trier
    n 1: one (as a judge) who examines and settles a case
    2: one who tries [syn: trier, attempter, essayer]